[Snowboarda42]

Welcome to the 40B club.

Personally, I'd stick with Metal Halide. You can stick with the 250W, you just need to keep it high off the water and maybe cut back on the photoperiod. Since you're doing a Canopy, look into a T-5 Retrofit Kit as well and get the best of both worlds. I wish I did this.

As far as powerheads go, get the Koralia 2's. I have 2 of them and I love em. Those alone will give you 30x Turnover (600gph each), plus the return pump will add a little more as well.

Since you're at this stage, I would get rid of the 20 Tall and get the 20L. Its MUCH easier to work in under the stand, and you can have a refugium, room for a bigger skimmer, and your pump will still fit. I would go overflow->Skimmer->fuge->return. Definitely go with a refugium of some sort, you won't regret it.

As far as Skimmers go, what are you going to get?