It is always good to start small and work your way up. Just remember, get a design in your head and test, test, test. And when you are confident, test some more.

I agree with Carlos, if you are building a tank where you need access to filter material occasionally, a canister is the way to go.

As far as a stand for the 90, simple, a piece of plywood the size of the tank, numerous cinder blocks (about $1.50 each at big box hardware stores) and a table cloth, and you got yourself a cheap, but ridiculously strong stand.