I've also got this plane and love it. I'm flying mine with a Saito 125, Futaba 6EXA and the S3004s that came with it, but on a 6v 1400mAH battery. I wouldn't suggest it. The torque is fine, but after 6 flights, I've already stripped one servo and I haven't even gotten frisky with it yet. I'm planning on switching to 3305s on everything but the throttle. With the 125, I bring it down after 6-7 minutes and I've still got about a quarter of a tank left.

I'll second the motion for the fourstroke. I'd suggest one in the 1.00 - 1.25 range. Mine with the Saito FA-125 and APC 17x4w prop will climb like a homesick angel and I usually fly it at half throttle most of the time, so I'd think the 100 would be plenty of power for you. And I didn't need a pump.