Two BL systems, need help

I've just recieved a feigao 540 8xl and a quark 125 monster pro for an E-Maxx and was told that I need a BEC even though the esc has one built in. Mike at rc-monster told me that the esc is only rated for 10 cells--- here's the spec's.

►Cells : Ni_Cd 5~18 cell
Lithium 2~6 cell
►Continuous : 125A ( @Full throttle, 25°C)
►Surge : 180A/design spec 300A(@10 secs)
►Switching Rate : 38KHz
►Resistance : 0.00036Ω+ 0.00036Ω
►Brake : Realistic ABS( Proportional )
►Low Voltage Cut-Off : Automatic
►High temperature Cut-Off : about 110~120°C
►Reversible : Completely Yes (Without change any wire)
►Timing Adjust : Automatic
►Safety : Full safety Mode with Master Recognition
Competition Mode with delayed Master Recognition
(Programmable with throttle position whenever power on)
►Program : On board Program button and colorful 4 LED
►BEC : 5.6V/5A (input : 8.4V, peak 8A)
►Size : 70 X 34 X 19 mm (Without wire)
►Weight : 78gram (Without wire)


1. Why would I need one, and what would happen if I tried to run it without one?
2. And how do those connectors go; should the male's go on the motor?
3. How do you solder the females?
4. Since the esc is for one battery and the E-Maxx runs on two, I'm gonna need to make a special pigtail for that--- right!