Giorgio: I do have a Pro, I have not had the time to mess with it yet (to create a CCF for it- I am still using my old CCF for my TS-1000).
1)I new you were talking about those four buttons, but from the picture the top two (without pictures on them) seem to be renamable. I am assuming that at least some of the other 6 (around the pad) can be reprogrammed, just not renamed.

I assume by "lager screen" what is meant is there is more of the screen to use. If that is an extra 10 or 20 pixels vertically, it might not be worth it to redo all your buttons, and you might just add 3-5 extra pixels between the icons (I found larger spaces between icons make it easier to use without looking, so I stopped crowding my screen a long time ago)

Some do use cover art, but even at 256 the result is acceptable. Gif, Jpeg would take less place, but they need more processing, and the more you shrink it (file size) the worst it looks.