Dude!

You are going to love E-flight. Tons of variables, props, batts, motors - etc.

The a-10 is cool, but will not be a spectactular performer. Those little fans can hardly make thrust! It will fly if you save weight. I think you should go with around 600-900 mA cells.

Reasoning- You must be able to have the right "C" rating. that is the safe discharge rate for any given battery. If your "C" is say 10 - then you can discharge at a max of 10x400mA=4Amps. You have 2 motors, each drawing close to that!
Your pack is light enough, but not beefy enough!

Other pack - too big. If it is also 10 C rated (likely for nimh) you can provide 15 A continuous, great! - but too heavy. It could work in many propeller driven planes, because you could tweak props, but I don't think there are as many options for choosing fan pitch.

Ducted electrics are cool, but are very underpowered compared to most model planes. It will almost be like a real airplane - no vertical, no save your butt power, less room for mistakes.

Good luck!