I thought I'd throw some helpful tips...so here. *This guide has area name spoilers for the first 2 arcs. None of the names have meaning except maybe a couple, so I spoiler tagged those just in case.

1. Collect Grass (they are all useful). Reach arc 2, grind Prince Points and pass the Nationalize Baths order. This will make baths free forever. (a lot of this can be used before then, but the bath cost amps up quite quickly, so it's not as viable before then)

2. Turn the bathhouse into your own personal workshop. Put your forge, crafting station, chemical lab and whatever cooking stations you want here.

3. To max forging and crafting:
3-1a) For forging, make a bunch of Broadswords (short sword), using 1 iron each.
3-1b) For crafting, make a bunch of Small Shields, using 1 iron each.
3-2) Upgrade your Broadsword/Small Shield with grass, specifically:

• LV1 Green Grass, from Selphia Plains
  
• LV5 Purple Grass, from Selphia Plains
  
• LV8 Antidote Grass, from everywhere
  
• LV11 for Blue Grass, from Selphia Plains and Yokmir Forest
  
• LV23 Black Grass, from Obsidian Mansion
  
• LV29 Indigo Grass, from Maya Road
  
• LV39 Yellow Grass, from Autumn Road
  
• LV40 Red Grass, from Delirium Lava Ruins
  
• LV48 Orange Grass, from Sercerezo Hill
  
• LV65 White Grass, from Sechs Territory

*Don't Upgrade past your skill LV.
**You get diminishing exp returns on using grass below your level, but you don't need to immediately move to the next grass upon reaching that difficulty rating, since the RP cost is still prohibitive and the increased gains aren't immediately noticeable.
***Once you've shipped a grass, it will be among the random selection to purchase in the flower shop, for 120g/each (less on sale). Just stock up like crazy. Arthur also sometimes sells them, at equal cost.

♦ Alternatively, fodder seems to give only slightly lesser gains than grass even at LV50, and for less RP cost per upgrade. If you don't have the Nationalize Baths order passed, or have a large stockpile of fodder, it's also a good option.

^You want the grass you are using to be next to the OK, so you can go between them with 1 button press. If using a controller, you can brush your thumb across both buttons to quickly load another grass and upgrade.

3) Upgrading without the needed RP will eat 1/4 of you health. You can upgrade 3 times by consuming health. Any more and you risk Jones taking 50% or more of your money. You might randomly get Nancy instead, who will heal you for free. Be careful.

4) Once at 1/4 health and no RP, walk a few steps, chat up Xiao Pai or Lin Fa and take a bath--recovering full HP and RP FOR FREE, and almost no time used (this also quickly levels up your bathing LV). With enough hearts you can party with them and do this all night if you want to. (I don't recommend this though. Better to stop around 5:50AM, warp to your room and sleep, cause you also want to LVL up Sleep too!) I maxed crafting from LV0 in maybe 1-1.5 in game days.

5) Maxing Medicine making and Cooking is slightly more arduous, since you can't upgrade. Just bulk produce recipes with few ingredients that you can mass farm. For medicine, use Grass-needing recipes when possible. For cooking, just fill a field with whatever. When you can make Strawberry Juice, spam that (it's a great money maker) until you can make Pineapple Juice (it's the second best money maker after Golden Juice). Don't forget the seasonal fields. They are permanently 1 season, so are useful for year-round whatever.

• Sleeping at 8:00PM is the same as sleeping at 5:59AM. As long as it is before 6AM, you are rested and get Sleep experience. ♦ I was incorrect. Sleeping before 6AM does fully restore you, but sleeping after 1AM does not give Sleep experience. Personally, I'd rather have the extra 5 hours /day.

• You can kill a boss, have its loot drop, gain the RP, then use the Return spell BEFORE the barrier disappears to have the boss respawn when you next enter on the same day. Good for RP/drop farming.

• During a typhoon, a unique monster (aptly named Typhoon) appears on the bridge below the Sercerezo Hill entrance (and warp). It is over LV100 (you can kill it with failed cooking dishes) and can drop a Mealy Apple (use the Return trick to farm it). The mealy apple severely lowers your stats and resistances when eaten or added to an item. BUT, if you upgrade with Object X (obtained by failing medicine making--reverses all further upgrade effects), it will instead increase your STR +100, VIT +150, INT +100, and all resistances except Love +10%. Farming Mealy Apples and loading a piece of equipment with them suddenly looks very appetizing.

• A tamed Typhoon has a wide array of dark and wind skills not available to the MC, and will curb stomp arc 2, but is much much harder to tame than...

• The fairy (I used 2 of to speed through arc 1+2 while very underlevelled) found in West Selphia Plains. It rapid fires its wind spell (Sonic Wind?) to shred, and often uses Prism--perhaps the most useful spell in the game. Using the tamer skill Bonus Concerto teleports your pets into your enemies, where Prism will annihilate pretty much anything not resistant. It has high M ATK growth on top of this.
^MC is also LV134, with maxed forging and crafting (which both increase STR) and has less than half the fairy's P/M.ATK/DEF. That's with up to date equipment (not upgraded though). This also does not take into account the Field Pendant accessory that passively increases pet stats, or the other tamer skill that increases pet stats for the entire day. Taming is real in this game.

• When charging the hammer/axe to hit all rocks/wood in a wider area, repeatedly hitting after the initial will keep hitting EVERYTHING multiple times. Items start disappearing after 20ish.

• You can craft/forge up to 2x your max RP in cost. It fails after that. Relax Tea is very useful for temporarily increasing your max RP.

• Scarves can be used to slightly decrease the production cost also.

• You can add additional materials into a recipe beyond those required. Up to 3 can be inherited into the item. The 3 are randomly chosen if more than 3 are used.

• Adding a weapon to a same type weapon's recipe will overwrite the recipe's base stats with the ingredient's. ex: Putting a Fenrir (LV99 glove) into a Leather Glove (LV2 glove) will create a Leather Glove with the base stats of the Fenrir. The Leather Glove requires less materials, so there are now more open slots for possible inheritance.

• Adding a weapon to a different type weapon's recipe normally won't do anything, but if a Light Ore is also added, the recipe's base stats will be overwritten. ex: Adding a spear and Light Ore into a short sword's recipe will give it the spear's base stats and reach.

• Adding an accessory into another accessory will pass on the special ability, but not the stats. ex: Rocket Boots with inherited Ghost Boots will have the movement speed increase of both.

• You can add a magnifying glass to any tool (either through the recipe or as an upgrade) to check soil and crop status without needing to switch equipment.

• You can add a Sacred Pole (highest tier fishing pole) to a tool to give it up to a 4th charge level (the normal max charge is 3). This charge may extend the range even further and costs no RP.

• Many materials give unique charge attacks to staffs when used as an upgrade. Of these, Dragon Bones (from the Revival Cave in West Selphia) is the strongest, without comparison. It replaces the LV3 staff charge with a summoned, persistent homing orb that completely ignores MDEF.

• Adding a Rainbow Watering Can to a staff replaces its LV1 charge with a useless rainbow, but tremendously increases the charge speed for all levels.

• Mass making equipment without the needed materials or forging/crafting with Scrap Iron will eventually produce Scrap Iron+, which decreases your inflicted damage to 1 (I usually use iron/weeds etc to craft shirts). Putting it into a weapon along with Raccoon Leaf and Glitta Argite (for increased range) will make a weapon that can hit a large area for 1 damage. In Leon Karnak, in a room on the right side are a bunch of Chipsqueeks (squirrels). Usually normal, occasionally a very slightly lighter coloured one appears. This legendary Mineral Squeek only has 4 HP *hint hint*. Damaging it causes it to drop either 2-Fold Steel (when used in upgrading, doubles the last upgrade), or more rarely the almighty 10-Fold Steel (increases the last upgrade +800% for a total of 9x, not 10x strangely). You. Want. These. If you use the Rail Strike arte a couple steps into the room, it will pull in all the enemies, hit them all 4+ times, and backstep you to the previous screen. Enter > Rail Strike > grab Fold Steel loot when it drops > repeat until sleep time.

• Gltta Argite comes from the Shining Tree. 2 screens left and 1 screen up from the Obsidian Mansion is a tree that you can interact with. It will randomly give a fruit tree seed or the Shining Tree seed.
  
• Raccoon Leaf comes from a boss in Sercerezo Hill only accessible during the first 5 days of each month. It is also the only way to get Sword/Shield/Dungeon seeds.
  
• Fold Steels can only be used once each while upgrading. Adding them to a recipe does nothing.

^It is slightly more pastel/washed out than the others. Hard to tell at first glance, eventually you will duck in and out of the room only rail striking when you see it.

• By adding a chain weapon and Light Ore into the recipe of a twin blade to change its base range, along with Scrap Iron+ and a Glitta, Then upgrading with a Glitta, 10-Fold Steel, Raccoon Leaf and whatever else you like will make Rail Strike pull every enemy on screen into a blender.

• Ailment infliction also increases ailment Resist skills. To more fully abuse this than the above (arc 3): Pick any twin sword recipe. Put a Fivestaff spear into the recipe (longest range base weapon?) along with a Light Ore and Glitta. Make sure all 3 are inherited (You can check with Barret). Upgrade with Melody Bottle, 10-Fold Iron, Glitta, 2-Fold, and whatever else. The first room in Rune Prana 5 has a ton of enemies. Rail strike or spam attack to completely debilitate everything. Exit and repeat, or continue spamming until Faint kills them. This will quickly level your Resist skills.

• Siren often drops her items into the water. You can fish 1 out. The others are lost?

• Forging and Crafting in this game is surprisingly deep. The " Be a Better Blacksmith [gamefaqs.gamespot.com]" pinned topic on gamefaqs's RF4 forum is VERY useful, and certainly worth a read.

Most of this was just to reorganize what I remembered on NP++. But if others find it useful, then I'm happy I shared.