I finally got my Saito FA-100GK ordered and the slimline pitts style muffler from hobbyhorse.com

(If anyone's from europe searching for a US supplier of Saito that'll post over to you - this is them!) They also are a distributor for slimline.
What prop size should i use for this plane for normal flight and for learning 3D flying?
Should i use a different prop for running in the engine?