I built on last year. I fitted a Fox .40 ABC in the nose. I added no weight anywhere. The battery pack and receiver gave me plenty of adjustment. I added turned down tips to mine for STOL. Never has tip stalled.
The fox is plenty for me 11x7 12,800. I wouldn't choose to go smaller than a bushed .40 or larger than a mild .46. If you want to keep most of your cowl your engine can get too large.