>>4490216Any specs or marketing will tell you, sometimes people use FX/DX also
Newer cameras have much better QoL features (USB-C, in-camera charging, wifi/bluetooth, etc) as well as better performance (IBIS, resolution, ISO capability, features), etc. Consider a 5D2 came out around the same time as the first iPhone, and see how different that technology is now.
For ISO, you want to look at actual sample images:
https://www.dpreview.com/reviews/image-comparison for a general idea. You should just always be at like 100 (or whatever's lowest on the body) for the staged shots, so this is really for the handheld museum shots. IBIS would help a lot there too.
>>4490217Typically would use a glass plate on top of the pages.
Lens distortion is separate from perspective distortion, so you just need to keep in mind both. A lens with low distortion itself, and shooting from an appropriate distance away (not to close or too far) that the pages start to look distorted (just like a selfie camera distorts a face really up close).
For handholding IBIS is great and can allow you to shoot at lower ISO's than otherwise, but your options are more limited within that budget, as almost no DSLRs have IBIS. So go for older FF or newer APS-C + IBIS (at least 24mp), D750 or 80/90D are where I'd be looking first on the DSLR side of things.