Wow. Sorry this sat so long. New job, and I need to feel out some time for RCU. I'm surprised nobody else chimed in on this one.

Anyway, I've gone through the process many many times in this forum, so you might get some additional ideas from skimming this forum. The basic rule of thumb is "Watts per pound." A plane needs a certain amount of power to fly in a certain way, regardless of what motor you choose. That's physics, Newton's Laws, and whatnot

Cubs have that magical ability to fly on a surprisingly small amount of power, but I would personally recommend a minimum of 75 Watts per pound. You'll need to estimate what the plane will weigh ready to fly, which can be tough, but the high end of the recommended weight range is generally a good starting point. Other sources of final weight are accounts of similar planes.

I'm estimating the plane will probably weigh around 5 pounds, which means you want at least 375 Watts at the battery. Let's do 400 Watts to make it easy and give you a little "reserve" power. 400 Watts is what the famous Gary Wright E3D power system puts out, and it's inexpensive:

10-cell CP2400 NiCd or GP3300 NiMH pack
Any brushed ESC rated for at least 40 Amps
Kyosho Endoplasma motor
Great Planes GD600 gearbox
10 tooth pinion from Model Electronics Corp.

Total power system weight of around 2lbs.