If you are playing with 6-piece live band don't bring arranger keyboard. It's very annoying that in a certain point in time you have a chance to accidentally hit the start/stop button. Yamaha MO8 is not bad. It has everything you need. If you need a second keyboard just buy a 49 or 61 keyboard controller. You can use MO8's sound engine. And you can tuck that little controller in one of the pockets of your MO's rolling case.

As far as monitoring on the stage I use Behringer ULTRATONE K3000FX. You don't need 15. 12 or 10 is fine. But I like I like my K3000FX so far.