[size=3]When you put some packing under the leading or trailing edge what you are actually doing is changing the angle of the fuselage and stab.
At a given speed and weight the wing will fly at the same angle whatever you do with the packing on the body.
What you have changed is the angle that the body flies at.
Adding weight to the nose to stop the nose up tendencies is probably the wrong thing to do.
The elevator has to have more "up' dialled in which tends to make it climb even more as the speed or power is increased. Fly it inverted and see how much down you have to push in. Should only be a little bit. Get help with that.
Getting the cg in the correct place is the only place it should be.
Your other problems are due to it being designed as a trainer and should not be regarded as problems if you are a beginner.
Find a good teacher, not a show off who wants to demonstrate "his" flying abilities with your model.
Just because you fly good doesn't mean you teach good.
Jim Fox