You're on the right track. OS 90 is a very good choice. I fly the 60 size ultra stick with a 90 and it is more than enough engine. Increase the size of the control surfaces. While you are designing them add balance tabs to the rudder and elevators. Take a look at the other successful designs for ideas. If you can add 4" of length to the fuselage. This will make the plane more stable and easier to hover.

EXCAP232