Irisaerial tried that a while back and had a problem with the whole washer getting hot and adjacent spots desoldering. did you experience that?
It was tricky, no doubt. The trick was to keep the washer cool as possible, and get the iron as hot as possible. Then just hit it with the heat, get it soldered, and be done with it. If you lolly-gag, it starts to melt adjacent sites. But I never had them actually pop off. I think it helped that I was using short pieces of wire that were not yet attached to the ESC's, so they had no stress trying to pull them off. It might help to actually drill holes in it, stick the wire in, so it's mechanically retained. Then it won't matter how hot you get it. But as I stated above, it sort of becomes a 1-shot thing. Which is fine, if you have to replace an ESC, you take the wires off at the ESC side.
Overall, the layout was tricky and time consuming the built. But it was really compact and reliable, IMO. You see I cut away windows for the heat sinks. The motor wires were wrapped in anti-abraision sleeve before going in the tubes. I put hot-glue as strain-relief where the wires come out of the heat-shrink on the board. Etc.
Your burst current must be up there. I've never thought of creating a CAP bank but maybe I'll try that, not that I need it but it sure would be fun. Just don't ground positive and negative together and you should be good lol..