Rust in the tank is not good, but it should not be able to get past the fuel filter - it should not be in the fuel pump (if your bike has one) and it should not be in the carbs.
The carbs could be full of gunk from the fuel evaporating out - but if the bike was able to run I would fix the tank first, replace the fuel filter (its probably plugged with rust) and the fuel lines in front of it, put some sea foam in a new tank of gas, and see how it runs, before you start pulling the carbs apart.
I dont know what it is with MCs and people ripping their carbs apart. I have owned 24 vehicles in my life, only the last 6 were fuel injected, and I have never needed to 'clean' or rebuild a carburetor ever. Nor do I know anyone that has. But for some reason MC riders will take their carbs apart at the drop of a hat.
Regarding your gas tank, see if you can find a used one and paint it to match before you spend a lot of money on the one you have. Once rust starts I dont think you can stop it in the long run.
Last edited by KCW; 10-19-2017 at 08:09 AM.