Are you planning on keeping fish in the set up?
How long did you have your 20G set up before you upgraded to the 40?
You'll need good lighting.
Good flow.
Probably a protien skimmer if you plan on keeping fish.
Those are just a few of the basics.
I'm planning on doing reef as well and I will definately be building a sump with a refugium in it. It will be housed in my aquarum stand underneath the tank. The sump will hold a protien skimmer, 2 heaters, a refugium and return pump. The doors on the stand will stay closed when I am not home so the dog doesn't get in it. Some things that I've learned while planning out my tank is that it takes patience, alot of research, money and a few fingers pointing in the right direction from our friends here at swf.com
A word of advise (not to discourage you) but be prepared to learn a few lessons the hard way. I know I have and that's why I try to do as much research as possible now before I buy or attempt to do anything with my tank. Ultimately I do want to have an awesome reef tank like many of the folks here but now I'm prepared to take it slow and save up my money as I am working towards my vision of the tank that I want to have and learning along the way.
Hey, you know anybody who wants some cichlids, mine won't quit breeding...
Quills