Scratch Plane

I have been working on a scratch plane that I designed and have a question for you. I'll give you the specs just so you can try to get a picture of it.
Wingspan-41"
Chord-8.25"
Fuse. Length~30"
Motor-Speed 400 w/ 3:1 gearbox
Prop- 9x6 or 10x7
Sky scooter 300Mah
Ok well my questions are, what kind of battery am I going to want, I have a Sky Scooter batter and I tried it out, It seemed to put out a lot of wind but not for very long. It only went for about 2 mins, but I don't know how much power I am going to need and that is another question. Is there any way to know how much air im gunna need to be pushin out? Also I have been trying the skyscooter battery but l don't know if it has enough power. Also it has no duration, doesn't last nearly long enough for a flight. If you have ANY help it would be greatly appreciated. If you need any more info let me know. Thanks all