• It doesn't matter what you're using, if there's latency you'll want to kill yourself. I have reformatted/reset devices just to get latency back down. Also, depending on your drawing style you might be more or less susceptible to latency issues (eg. the faster you move the less effective the digitiser will be).
• Fiddling with the default settings for a digitiser has never yielded better than out of box performance for me.
• I've never noticed much difference with pressure levels and I've used tablets back when they were 1024 levels and less. Again, style may be a factor.
• Processing power isn't the issue, a digitiser is just a fancy mouse. Plenty of wacom tablets used to come with mice using their technology that you just used on top of the tablet. Now lots of them are multitouch touchpads as well as digitisers.
• The aspect ratio of the digitiser and the screen should match. Yes, you should double check that even if you think you don't need to.
• There are plenty of real computers (ie. laptops) that have decent (read: wacom) digitisers in them. Things can be portable and still computers, but you're going to have to be rich, make compromises, or both.
• Ipad + apple pencil + procreate seems to be a combo that a lot of people like. I want to investigate that myself but covid got in the way and I'm not spending that kind of cash without a test drive.
• Doing it properly usually means wacom digitiser + desktop + photoshop. Wacom display (cintiq) if you can afford it. You see this set up time and time again when you see people that do it for a living.
• Cheaper options may work for you, but this is one of those areas where tactile, and hand-eye experience is critical. I've found that you just have to eat the expense in buying and trying a lot of the time.
• I have a cheap wacom digitiser for when I feel like drawing + whatever paint app I'm messing around with. On pc. The digitiser can do bluetooth and I generally don't care about that, but it's worth mentioning that the wireless experience is indistinguishable from the wired for me.
• I use a boox note with an epaper display and wacom digitiser built in, running android. Plus a third party pen because their own pen is short and thin, and the tip is slippery. I wouldn't describe this as a perfect setup because only boox's own apps implement their fast screen updates (despite the SDK being freely available). It's a device that is screaming out for better software. I don't use it for drawing, just diagrams and writing.
• If you want a third party pen expect nobody to give you a straight answer about compatibility.
• I expect the epaper writing tablet ecosystem to improve over the next few years. That being said, it's a niche and it shows.
• Everything new will be usb c. What I want to see more of is wireless charging for mobile devices. I still have to plug in the boox but I can throw my phone on a qi charger. It's a convenience feature rather than a showstopper.
• Never underestimate how dirty something made from plastic or glass that you're touching non-stop will get. Take whatever filth mitigation measures you find tolerable.

I know you said android, but I use an iPad Pro and am quite happy with it. The biggest thing affecting drawing performance is pad-to-screen latency, and Apple has actual experts that have spent a lot of time on that problem at the OS and hardware level - I don’t think android is well set up to achieve anything similar because of OS/hardware disintegration.

I sent the book cover for the Tab S6 back, because the shortcuts are stupid. Like I can't press super+d, I have to press super first, then d. But I'm using a G915 TKL with it, and it doesn't have that problem. (switching between computer and blueeoth/tablet mode is extremely quick)
I don't quite understand the shift+space issue. As I also type fast, but never noticed pressing both keys at the same time. Maybe it's also not a practical issue with an external keyboard, as the book cover is just wonky as heck.