Arch w/ KDE gamer here. I have generally had a good experience with it. I think everything you said is generally accurate. In terms of customization, lack of bloat, and a good wiki, Arch is generally considered to be all of those things. A rolling distro like Arch I believe will also be getting the latest proton updates, which may help with sooner game compatibility/optimization updates on more recent releases.
I say go for it.
I would say a used Dell or HP business laptop would be a safe bet. Most business laptops have decent keyboards, replacement batteries will be relatively easy to find, and user-serviceable RAM is the norm. Given the not especially high processing power needs, probably the middle-specced ones with a few gens-old i5 will be dirt cheap and work fine for your needs.