Keep the plane light and you'll love it. This plane is the exact same plane as the Seagull Extra 300. Same build, same components, everything is the exact same(except internally, the pushrod guide tubes on the seagull are metal cased with plastic tube inserts). The color schemes are also the same, except the SZeagull uses black where the Graupner uses the blue striping. If you need replacement parts for your graupner for whatever reason, you can use the parts from the Seagull. They can be obtained form Horizonhobby.

I put a Saito FA90-TS(twin) in my Graupner. Engine produces 1.2HP. That motor is the same weight as the recommended 61 two stroke on Hobby-lobby's website but a good increase in power. The TT61pro produces 0.85HP. You may way to go with a 91 4-stroke to get nice power with room to spare. The 61 is the minimum I'd fly that plane with. You sohuld also consider putting in a bigger fuel tank as the stock 6.5-7oz tank is really too small...even for a small 2-stroke.
I put a 16oz boat tank in mine becausde it was slim. Its a Sullivan "Vee" type boat tank. Works great....only modest modification to get it to fit in the fuse. I can take a picture of my setup if you want.

You'll also probably want a larger prop then a 12x6 as that will not really have enough thrust for decent vertical. A 13 or 14 would be better. So, my recomendation is get a 91 4-stroke....or a larger two stroke cuz you'll really want more power then the YY61 will give you. Keep the weight of the plane under 7.5 pounds dry. At close to 8 pounds, it will have a tendency to drop the left wing if you get too slow(ask me how I know). Mine weighed 7 pounds 14 oz because I had onboard glow for use with the twin 90 plus the extra battery to power it.

I now am building the Seagull version as a replacement and am using the Saito [email protected] HP