There was a thread a while back about this that I'd rather forget!... but if I can find it, I'll post a link.
But in a nutshell... do whatever the tank manufacturer recommends. In my opinion, if the tank is designed to sit on the frame, then that's how it should sit. If you support the glass you are asking for trouble and a broken tank.
Regarding insulation under the tank, well... I'll try and find the post.
Ugg... I found it: insulation pad or not?