Welcome to 3D flying ... its fun. There are a few kinds of 3D planes:

i. scale planes (Extra, Edge 540) - they are built with larger control surfaces and lighter for 3D
ii. profile planes - what you see at OMP
iii. typical 3D planes - like Funtana, Magic etc

What is good to start with will be something that wants to prop hang easily. I find one the many planes I have flow it is the TT Spirit that hangs so easily. It also has no bad tendencies to snap when you push her hard (in short when you yank the elevator fast).

As for engines 4C is in now, best buy is your Saito 82 and you can also go for a YS63 if you feel rich, 2C engines are good also, you are best off with an OS50SX as that gives you a lot of extra reserve. The engines like TT46 will be fine for any plane of 4.5 lbs to 5 lbs.

Prop wise you can go for:

46 2C - 11x5; 12.25x3.75; 12x4
50 2C - 12x4
72 4C - 13x4W
82 4C - 14x4W

What make is your SU31 and Extra? I have seen trainers doing prop hangs even. Hehehe ...