I have tried to avoid as much spoiler stuff as possible, please be aware that you will find about certain content that unlocks with progression by reading this:

Quick start hints, PS I overnight AFK (Phone and Steam):
*Early game: Use 2x Nurse and 3-4x Carpenter to lvl25 asap(then keep going to lvl50). These are perfect for late game too, I swap 1x Carpenter for the Special character at end game. (invest +HP +Physical +class relics to progress).
*ALTERNATE setup: that suits lategame: 2x Nurse + 4x Darkmage (invest +HP +magic +class relics)

Early game
*Invest in "relic of health" asap; level 100 to max 400 for progression only. Add more here late game.
*Invest in relic of attack asap too, if you kill things before they touch you, you wont need health ;)
*Invest a little into the "relic of mana" at the start, just to keep your nurse mana pool up long enough between Healing Fairies, 100-200 should be enough. If you play actively, you could skip this if you don't mind building your team constantly when they run out of mana. stating the obvious here, but it is more efficient to have your team alive and farming, so I prefer to dump points into the mana pool for progression.
*When you get the mana regen gem, socket that to both nurses and stop investing in mana. You will not need mana regen or pool shortly after you unlock class relics(level 50).

Late game Relics:
*Class relics, focus on your dark mage OR Special unlocked character when you get it.
*Special char + Nailers: Invest in their class relics: and even out the extra essences into
*Gold find - this is where you will progress faster, it is worth investing here and stacking with gold equipment. I get way more essence from gold than from essence drops (even if I equip essence pet+gear+max essence find).

Secondary Relics:
*Dungeon keys: Useful to some degree, but does require a standard hit to proc
*Relic of mastery, useful for leveling, useless once you are leveled.
*Relic of Ore, AVOID points here, this cant be undone and later you don't want ore!
*Resistance: Very useful, even early game. Sleep is annoying.
*Reflection: Not useful really, you will be killing everything before they hit you(hopefully)

Notes of interest:
*You will get all relics at late game so just pick them in the order you fancy.
*I don't crit with skills, certainly "special character" and carpenter skills don't crit for me. It seems only relevant to standard attacks. So don't bother to invest in crit relics.
*+HP Regen is useful early game, meaningless late game.
*+Essence relic is worth it later, I capped it much later for the passive income.
*+Gold is meaningless early game, outstrips essence gain later game as it's uncapped.
*+Physical relics affect spells that are physical spells.
*Healing fairy restores mana/hp, but wont revive dead team members.
*You wont need to mine resources later game, arguable you don't need it earlier either - you just find better gear too quickly.
*Special Character unlocks at W levels(you'll know what that means when you get there).
*You can transfer between Android and Steam easily, very quick too.
*Achievements are possible to transfer, just hit that "report achievements to server" button and restart.

Unlock the soda scripts:
*I highly recommend a script for each character.
*All my scripts are between 2-4 lines, you only need AFK scripts, which are simple:
Heal then Defend (nurse),
AoE Attack (DL/Dark mage),
Nailer skill(Carpenter).
Defend (for leveling characters).
(Let me know if you want the exact scripts)
*Edit*: Please see updated script advice here: https://thesovietgaming.com/soda-dungeon-2/soda-dungeon-2-warriors-dimension-scripts/

Character layout:
I found best order is: (special), nurse, nurse, nailer, nailer, nailer (+nailer before special unlocks)

Crafting:
*Crafting is not needed, byt he time resources were available, almost all crafted gear was not useful any more.
*I only crafted char XP gems, a couple sleep gems for nurse - not even sure they were that useful.
*I did craft Gold+ items for my AFK farming.

Pets for late game:
*Gold+ for framing
*Dodge+ if you are stacking Dodge
*Reduced damage+

P2W?: I did invest early in most things, it really isn't needed, it isn't a pay-to-play game, but is a pay-to-lategame quickly.
A few I would invest in would be -Adverts and quicker battles.
Don't bother unlocking sodas, it's a complete waste. I also wouldn't burn caps on relics; if you really want to burn money, *maybe* when relics cost 1600 essence each level, it's just too easy to get essence, especially later. It doesn't save much time.
Building upgrades seemed worth it for time saving to me, but I just cant tell you what it looks like if you don't invest in buildings (maybe someone comment if they did it)?

Hidden Achievement hint:

*Miner + Dark mage skills are needed.

Hidden Achievement Answer:

*Do this manually, use a Dark mage lvl25 skill to curse a mob into stone.
*Use the Miner pickaxe skill on the cursed mob, job done.