Make one change at a time, or as close as is practical, and make small changes at that.

In your case, I would get the c.g. adjusted, (maybe add some expo to the elevator too?), and lean the engine to peak power. If it is well over 7500 rpms static, then yes, you should prop up. Go to an 18 x 8 in that case, not an 18 x 10. If you go to an 18 x 10, you might have problems getting it slowed down for landing, among other things. Get the airplane dialed in a little better, get to know it, and then continue making changes if necessary.

Enjoy it!

AV8TOR