6 buttons + dpad at a minium should be fine as start + select can be keys on the N900 as you do not have to use them often.

Most games dont even make use of all 6 of the main buttons so just depends on the game.

Anyways, there maybe hope in this product I mentioned it once before but I think that post/thread fell into the abyss:

http://go.notebookreview.com/?id=525...23ht_917wt_728

Its a direct connection via usb for 2 wii classic controllers it works on almost all PC platforms, but no drivers for linux. Since the N900 has a usb port, with an adapter and a good devolper chances are this product will work.

I just ordered one but I have no clue how to program it to work on the N900 and I highly doubt it will be plug & play (though it may show up has a HID device...)