For me, the X270 ist the sweet spot: it is small and portable and has a acceptable battery( in fact 2 of them). The display is usable and comes in full HD. 720p is a little bit too low for my tastes. You can upgrade the RAM and put an m.2 ssd inside(although only with 2x PCIe bandwidth). You can also charge it with USB-C. With an i5 it goes for around 200€ in Germany. US prices are usually lower.

Thanks for your work and don’t push yourself too far. I‘d prefer a good and carefully written app in a few months over an unstable und hasty written on in a few weeks.

At least Mlem, the app for iOS is explicitly compatible to all accessibility functions in iOS. They wrote in their latest changelog that they have someone auditing their app to be compatible with this stuff.