Welcome, I hope you see this project through, it looks like one that needs a lot of TLC and would challenge even the wisest of souls here. Rusted tanks are not a big problem, you can make the rust inert and coat it. When done properly it won't cause any issues.

I'm embarking on a similar magnitude project on a different bike so I think I will be sharing similar frustrations to you.

The forum is a bug source of knowledge, so continue to search and ask as you go.

Good luck!