I also had a problem with my fuel tank installation. I surrounded the tank with a lot of old foam bedding material and secured it in the rear by inserting a diagonal piece of plywood between the tank and the former. I plumbed the tank for a three line fueling system. The fuel leak I mentioned was a result of the vent line being severed when the tubing hit the back of the firewall during tank installation. To resolve this problem, I glued a piece of balsa behind the firewall to prevent the tubing from hitting the firewall. Good luck with yours. I think you will like the way it flys.

Buy the way, I mounted my battery as far forward as possible under the tank but still had to add nose weight to the firewall.

I didn't do any of the modifications you mentioned but probably should have.