Move your receiver battery back as far as you can. This will help balance the plane a little better. You can fly it somewhat noseheavy without too much penalty, it'll just land a little fast. I wouldn't add extra weight to a trainer. If it still seems too nose heavy (as opposed to just somewhat nose heavy), you should seriously consider buying a lighter engine like a .46 LA or a Thunder Tiger Pro .36.
As far as props, an 11x5 APC sport prop should be a good match for your .46 AX. It will provide a decent amount of load so the engine won't rev too high, it will help the plane takeoff and climb out quickly, but it won't build up a ton of airspeed because of the 5" pitch. This prop will work with most any 2-stroke sport engine in .40 to .56 cu in range. Your .46 AX should normally peak out around 12K to 12.5K with an APC 11x5 sport prop.
The problem you describe with the power switch and the receiver makes me believe that the hole for the switch isn't cut out quite large enough and that it might be pushing the switch slightly over to the "on" side by default. The power switch for the receiver battery should snap crisply in both directions; if not then get a new switch.
Hinge gaps are fairly important, even on a trainer. You should seal the hinge gaps with clear packing tape along the control surfaces. This will improve the effectiveness of your control surfaces and help protect them from getting torn loose from "flutter" if you fly at higher speeds. Your .46 AX will test your CA hinges plenty well, even with an 11x5 prop. Push the control surface full up to apply tape to the bottom of the control surface, then move it full down and apply tape to the top.
Veteran builders will use Monokote to seal their hinges; if you feel up to the challenge you can forego the clear packing tape. The tape won't look as nice but the plane will fly better and nobody will notice it unless they get up close to look at it. I'm more concerned about my planes flying good than I am worried about style points, but that's just me.
Your overall set-up looks good; you're SOL on the $5 though!
