1. Kobo ereaders are dirt cheap at thrift stores (and run Linux)
2. KOreader is simple to install (I have done this)
3. KOReader has a text editor + terminal built in, and has a setting to switch to USB-OTG mode, which should allow you to plug in a USB-C hub, and a mechanical keyboard.
Boom! Internet connected e-ink writing tablet with excellent battery life, and the best keyboard you have, for ~$5-100.