I think you need to get 5 of your best on the floor and go from there. You can really put subs in a specific rotation as who comes in depends on many factors- who may be struggling, who may be in foul trouble, whether the other size has a speed or size advantage, whether you need a shooter/ballhandler/rebounder, etc. Much of the rotation troubles could be remedied by Harney shaking the attitude and playing hard all of the time, as he can play multiple positions.
At this juncture, I would start Diggs, McAdams, Forsythe, Tree and Harney. Kretzer, Johnson and Evans would be my first options off of the bench, with Betancourt, Ibatayo an Cheahtam only seeing minutes here and there.