[frizzen]

I don't have any hydro excavator, so i'm answering in general.

Don't feel bad, I think everybody here has let the smoke out of some parts at least once...

0
Pull red wire at rx plug from *ALL* the esc, test again with the bec powering the rx. Some might come back to life.

1
There are some chinese Sabertooth style dual channel mixing escs, but the reviews seem to be typical for Chineseium. Some are flawless, some go poof. How many amp do your motors need?

The motors can't use more amps than they're rated for at stall, if you go with a much bigger esc it can reduce the low speed control some.

2
The white wire would be for signal, bec doesn't care about signal. Keep or delete it as you feel like

3
Uh. I hope someone has done a walkthrough on that radio already, plane to surface setups are confusing.

4
Doesn't matter. The lipo 25c means it can charge/discharge at up to 25 times the capacity. So a 1Ah 25c pack could do 25Ah if it had to. A 1Ah 1c can only do 1Ah state of change.