I like your tank. Careful with that drilled hole. Looks like it's spidering around the edges and is oblong. Hard to tell from the pic though.
As far as a skimmer, Reef Octo is a good way to go. If you are going in-sump, you may end up having to build a platform to get the skimmer set at the right water height. The inner walls that you siliconed into the 20 sump are on the high side. Lighting is tough because of the dimensions of a corner tank. If you are going reef, I like metal halide (400 watt with supplemental actinics). Many people are into LED
's. I'm not completely sold on their ability to "grow" corals over time and getting the color/temps can be tricky. Appealing to the eye doesn't translate to coral growth here.
What are your plans with the tank?