This is the best choice IMHO. You have a rock solid OS (Debian) and all possible taken measures to harden it with Kicksecure patch.
Windows... With this only word you already have all the abswers
Well, GIMP is great but uneasy, not sure but Paint.NET on Windows is simpler but very user friendly and may be sufficient for your needs
Absolutely every website you visit or app you use, if they track such info of course.
Can you tell us why Qwant wasn't a good choice for you? I heard they work hard on respecting privacy while providing good results... So I am curious about your experience
Not worse, but less repeatable. You don't see any difference in typing, it just help reduce fingerprinting
Keyboard is absolutely a thing to be careful with. On Android mobile, use OpenBoard for example. On computer, if you use Linux, also install kloak [https://github.com/Whonix/kloak], a tool that slightly delays randomly your keystrokes to help you hide your typing pattern that can definitively identify you
It's important to distinguish privacy, anonimity and security.
Choose a smartwatch that supports Gadgetbrige, a free, open source and great OS for smartwatches
Change iSP if you can, ans un any case you should use your own router running OpenWRT to have full control over your own network
Dell provides XPS laptop with Ubuntu on it. It works great and Ubuntu can be replaced with other distro ( I did successfully tested Mint and now Debian 11)