Restarting my tank - need expertise

So about 5 years ago I took apart my reef tank because I knew going back to school I wouldn't be able to keep it.
It was a simple 72gal bow setup with a hang on the edge protein skimmer. Basically I went to the fish store, the fish store guy said "buy this" and I did.

Now i've done a bunch of reading, but I need some things clarified and maybe some suggestions.

I want to go with a sump and have as little UN-neccissary equipment in the tank as possible for visual reasons only. Second is I would much rather not drill my tank and was looking at a reeflife system.
Now my understanding is that only the prefilter box goes into the main tank, then drains to the sump, so one question I couldn't seem to find a straight answer to is can I run the protein skimmer (planning on upgrading from what I had) in the sump only?
Also I assume I can put my heater in the sump and the return pump will just add the warmed water back to the main tank?

I'm sure all this has been answered before, I just wanted to get some 100% answers before I start dropping $$ and killing fish. Thank you