My last question on brushless system

So I decided to buy two 3s2p packs and wire them in series. But the only problem that is left is that I am worried that the individual cells in each pack may discharge at different rates. And though my lvp will detect if the pack goes below 18 volts (3v per cell), it won't detect the individual cells voltage. So while one cell is at 2.2v, and the other cell is at 3.9v (or something like that), I could be looking at a destroyed lipo.

Will a balancer solve this problem?

I'm buying from maxamps. Anything they sell will stop this?

Should I go 10xl, or 9xl with this setup (10xl is in stock at rcm). I will most likely be running either a 12020 or a 20150 micro car.

Are the gold plugs preinstalled on the lehner motors able to be swapped with 5.5mm gold? If so I may go with a 2240 or 2250 hiamp. Speaking of which, what is the KV rating for the 2250 hiamp, and where do I buy it?

Thank you!