Instead of a twin aerobatic airliner, I would like a four engine version instead.

How many cells should I need for flight times of five minutes with proper throttle management?

Or should I go for four S280?

It depends on how big your airplane is going to be and if you are going to fly it direct or with gear drive. Seven or eight cells will be enough to power the motors in either case but the size of the milliamps will be up to what the plane can carry. The advance notice on the Multiplex Cargo is a seven cell battery for 4 400s. Hope that is some help.