I would say switch the prince to a demon of Nurgle. While he is in the air he has a 3+ cover save.
You dont really have anything in the way of melta guns, not counting the oblits as they should be pounding away on other targets. Also Your lord really should have something that makes use of his WS and melee abilities, even if its just an ap3 power weapon or lightning claw. Im thinking drop the combi plasma off the lord and give him a lightning claw and blight grenades, and give your bikers melta guns instead.