Outline:
1. Framerate Problems & Related Fixes.
2. Black Screen on launch/Alt-Tab during gameplay fixes.
3. Loss of Weapon Selection In-Game.

Disclaimer:
I'm mostly writing this for my own personal reference, but if it helps you out then I'm glad that a good thing happened. I doubt this will be a perfect fix for any one person's problems - the game seems to have multiple bugs based on rig configurations, and everyone on the Internet has some sort of magic solution for its various problems.

If I ever want to replay it (doubtful after this experience, but who knows), I want to have something to refer to since it took me two days to just setup and get to basic gameplay. If Steam had a notes feature in 2018 then I wouldn't have to publish this at all, but not yet so far.

What a joke that in 2018 Ubisoft is selling this game with this many bugs, much less on major Steam sales.

System In Use At Time of Play:
OS: Windows 10 Home 2004 (May 2020 Update) Build:
CPU: Intel Core i5 4690K @ 3.5Ghz (Stock - Summertime Temps)
RAM: 16GB DDR3 @ 666Mhz
Mobo: MSI Z87I GAMING AC
GFX: MSI NVIDIA GeForce GTX 1070 GAMING X 8G VRAM
Driver: GeForce Game Ready Driver Version 398.36 (Released 6/26/2018)

A humble system for when this guide was written, but decent enough to run something from 2013 at 1080p.

Guide To Follow:
"Silky Smooth 60FPS Guide"
https://steamproxy.net/sharedfiles/filedetails/?id=508912001
Credit: LestatLestotis

Addresses issue with V-Sync and Triple Buffering Problems preventing 60FPS performance in-game. Found to be better alternative than attempting to Alt-Tab or temporarily lock screen solutions.

Conjecture: Perhaps something in Windows 1803 Build renders these solutions ineffective with this GFX driver set?

Guide Contents (Relevant portions reprinted in case of deletion/removal):

Nvidia Control Panel/Catalyst Control Center Options:
Program Settings directly for AC4BFSP.exe (Global Settings were ignored, I don't want this for all my games)

Maximum Pre-Rendered Frames: 2
Power Management: Prefer Maximum Performance
Negative LOD Bias: Clamp
Threaded Optimization: On
Triple Buffering: On
V-Sync: On

In-Game Settings
(Do this immediately on first successful run to main menu, before starting a new game)

All options maxed out* except:
PhysX Particles: Off (Implementation of engine seems to be poor)
Shadows: Very High (In lieu of Soft Shadows)
Anti-aliasing: TXAA 2X
V-Sync: Off (Note the difference from forced driver settings)

*I dropped some of these down to "very high" in some cases for my own benefit.

Third Party Programs:
Riva Tuner Statistics Server with a frame limit of 60Hz
(Not enabled, or used in my case - trial and error led me to realizing this was of no use to me at the moment so I opted to ignore.)

D3DOVerrider: Forced V-Sync, Forced Triple Buffering
Enable at login, make sure it is on prior to launching program.

Overview:
The game has a serious issue in this OS build that prevents the game from launching. Multiple suggestions online about "verifying game files" and deleting certain patch files (DataPC.Forge, BitGuard, etc) but given the timing of these posts (circa 2013-2014) I suspect these are not relevant or related to the current issues in 2018, especially on my build. Multiple attempts at deletion, renaming, and reverifying (including redownloading the game)

Error Log:
System specifically showed problems when launching through Steam Client (displayed as "Running" but would not launch anywhere else, despite showing as a running process in Task Manager.) Upon realizing that "UPlay" was needed to also launch the game, I attempted to ignore steam, and open through Uplay. Successful launch to main screen with visuals.

However, upon closing and attempting to re-open, the game would show a black screen. Background sound, and menus would seemingly load (audio effects can be heard), but nothing else would show. Alt-Tab to desktop and force close and reopen would result in the same problem. Full reset of system would allow for successful boot, but upon any further subsequent load without reboot, the game would black screen. Unacceptable.

Fixes:
In certain cases, launching directly through UPlay alone was unhelpful (Black Screen). The following processes seemed to have alleviated the black screen issue to an acceptable degree (multiple launches possible without system reboot)

In the respective game directory and UPlay directory:
1. Set "UPlay" and "AC4BFSP.exe" to launch with administrative rights.

In UPlay:
1. Uncheck "Enable cloud save synchronization for supported games."
(Apparently this is not supported? Unclear, and haven't had a chance to re-test as of writing.)
2. Uncheck "Enable in-game overlay for supported games."
3. Under "Notifications", uncheck "Enable In-Game Notifications."
4. Uncheck "Enable Desktop Notifications."

Game seems to launch easily, which makes me suspect something is wrong with UPlay overlay interface and graphics in my case. UPlay will warn that game is launching without overlay. Ignore and proceed.

Upon any Alt-Tab scenarios it seems black screens are still normal in which case a complete force quit of UPlay, and Steam is required. Relaunch from desktop icon. No system reboot is required.

Unable to select weapons via "Q" or Mouse Wheel. Rebinding or resetting. Idiotic bug.

Follow this guide based on a Reddit Thread (See Post 4 on the thread):
https://forums.ubi.com/showthread.php/812798-How-do-you-switch-weapons-i-e-a-gun-etc-I-m-encountering-a-glitch-Forums

Guide Contents (Relevant portions reprinted in case of deletion/removal):
1. Go to your documents folder and find the Assassins Creed IV Black Flag folder.
2. Open the Assassin4.ini file
3. Find the lines under [KeyboardMouse2 DefaultBindings]:

PadUp=-1

PadRight=-1

PadDown=-1

PadLeft=-1

4. Change these lines to:

PadUp=72

PadRight=77

PadDown=80

PadLeft=75

5. Save the file.
6. Start AC4 Black Flag and load your game
7. Use the numpad keys 2, 4, 6 and 8 on your keyboard to select weapons

Your weapon wheel (menu) now shows up and you can select the throwing knife!

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End of Guide
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