I mean in the end I'm just making sugestions. You have to decide yourself what your priorities are. Either way I do hope I will be able to read your books for a long time to come.

Well, practice makes perfect. Question is how much of your health are you willing to sacrifice for speed. I would assume if you were to start writing on pc it woud take little to noticebly improve. Also blue-light filtering glasses would be worth looking into.

Laptop? Portable computer?

Personaly I would prefer #2 but as already mentioned going with #1 whenever you are tired seems like a good idea. Also you realy sxhold consider getting a notebook. Writing on your smartphone can't be healthy in the long run.