My piper 3 uses the engine range btwn .20 to .28 stroke engine..can i have a .35 FLASH engine mount on it and yet not cause any imbalance or sort??
Probably. Most .32-.35 engines are simply .28s bored out.

is this suppose to be normal cause when the engine is mounted, the engine seems to tilt to the right a little.
Some trainers use right thrust to offset the torque produced by the engine, which tries to turn the plane to the left. "Right thrust" means the engine is angled with the prop shaft to the right when looking down at the plane and standing behind it.

To start the engine running shld i get a 12V startter or jus manually using a dowel....??
That will depend on how easily the engine will start. Some engines start readily with a "chicken stick", some need a little kick from an electric starter. If you use a chicken stick, DO NOT use a bare wood dowel, you may damage the prop. Get one of the cushioned chicken sticks readily available from your LHS. Also, GET AN INSTRUCTOR!!! You'll be a LOT happier and your R/C learning experience won't cost as much.

Dr.1