I made a lot of progress today. Most of the thick wires are soldered.
I polished the VESC with ever finer getting sandpaper. The original looked flat but was actually very cupped. Now it should make a good surface to transfer the heat to the ESC housing.
Two buttons were added. One for the UBEC and the second one as a start button.
The ESC box is full of holes now. Different sizes for different cable connectors. MY XT150 cables will fit through, but without the plastic housing. Bullet connectors only.
I installed the main fuse.
The motor wires were soldered on. This is AWG 8 to AWG 12. The VESC and motor both have AWG 12. Nothing I can do about it I guess. But all other cables are future proof if I get a more powerful ESC.
I waterproofed the connection by coating the solder joint with silicone and then adding heat shrink tubing while it was still fresh. I will add a second layer when longer heat shrink arrives.