Well, while I presume you meant to say less than 400$, if you really did mean more then I would highly recommend getting a Framework laptop. They are amazing fully repairable and upgradable ultrabooks, and they have mostly excellent Linux support (you can even buy them without windows preinstalled!). I’ve had one for several months now and it’s been great.

Yeah, I’ve used Okular for a while now on my desktop and it’s generally been fine (definitly far better than GNOME’s pdf reader), but I’ve found it’s text insertion routine to be a bit finicky (although it’s possible I may have missed a better way to do it), and I don’t think it’ll work well on a tablet. I will still give it a shot though once I can!

Proton has a great free tier that may work well for you. I’ve used them for a while now and it’s been great. They have what is probably the most feature-complete private email service out there (unless I’m forgetting something). The main nitpick I have with them is how little they focus on Linux, but that applies more for their other services than email.