There is no fullscreen support for the P800. You'll have to deal with the keypad, and the "measly" 208x172 (that's a lot for mobile development).
and also green, pink, yellow and blue buttons (which I cannot get the specific keycodes for - does anyone know of them as I use -6,-7 for the green crossand red tick which work on the emmulator?)
You can catch them as game actions, they map to the GAME_A, GAME_B, GAME_C, GAME_D game actions.
but I have heard that MIDP 1.0 phones can get access to MIDP 2.0 specific features by being built with j2mepolish
Not the fullscreen. What you're thinking about is an emulation of the MIDP 2.0 Game API (so you can use Sprites, Layers, etc.).