Hi!
Might I suggest that you post your question over at "General Arranger Keyboard" forum. You will get a lot more help there.

I'll try to do the best I can to help though. Personally I don't use anything with less than 61 keys (five octaves). My main studio master controller keyboard is a fully weighted 88-note Motif ES8 and as awesome as it is for studio work I wouldn't want to take one to a live gig. Size and weight will pretty much outweigh it's awesome keyboard feel and response. If you are going to play live I suggest you go with either a 61-note or a 76-note keyboard. Can't suggest anything specific since I personally don't use arrangers. For that you wil have to ask guys over at GAK.

Good luck.

-ED-