As far as the battery goes, 4s means 14.8v nominal... typically ~13.5v-14.0v under load. Your 6lb plane could use 840W = 140W/lb. You need a pack with sufficient capacity (mAh) x C-rate (20C, 45C, whatever) to provide whatever your motor/prop combo draws. If you have an 80A ESC then you won't want to draw much more than 60A... something like 4s 20C 4000mAh (~80A) or 30C 3000mAh (~90A) would do nicely, but as long as weight is not too much of a factor bigger is better to give yourself more headroom... 20C 5000mAh (~100A) would give you longer flight times. You need to choose a prop which, with that motor and a 4s pack draws ~60A. (60A x 14v = 840W).

Most people seem to use 5s or 6s on that 400Kv motor... that would keep the amps down to a more comfortable level for it... it is rated for 68A max.... something below 50A on 5s or 6s would be good. A 14x10 on 6s is said to draw 47A.