RE: Can´t get the static margin right
As near as I can figure, at a slow flying speed of 30 MPH, you'll be getting near 55 lbs of thrust. With 15 deg AoA, that's about 5800 oz-in of nose up torque, worth about 0.4 lift coefficient on the tail. I would say your power on neutral point should not exceed about 5" behind the wing aero center (almost 11" back from the LE). If your CG is 7", your margin becomes closer to 17%. You'll really only know for sure by flying it! Interference between the fuse and stab could have a negative effect on stability as well.