Eheim 2213 vs. Fluval 204 ??

If you plan on corals in the end i would setup a refugium. with any canister you will have nitrates unless you clean it at minimum once a month. IF you wanted to just run a skimmer you could do that. Get a good HOB skimmer like Remora. If the tank isnt drilled which i take it isnt, then you could do with a HOB refugium and skimmer which will be enough for that tank. Power heads - most like maxi jet, I use a different ones.

Both of them are fantastic filters UNTIL cleaning time, then they become the biggest pain in the butt you've dealt with, then eventually you'll dread cleaning them, get lazy, nitrates skyrocket, tank gets grungy, then both of them stink as filters. Mind you, it's our fault, not the filters, when this happens, but they're a pain to disassemble, clean thouroughly, reassemble, and reinstall.

Yes, certainly go with a refugium. Be sure that any foam skimmer you use isn't connected to the fuge. You want the critters that grow in the fuge to flow unfiltered into the tank. And don't skim the water going into the fuge either, as you want tank water going into it. Try (if possible) to have the skimmer on a different water circuit than the fuge.

For mechanical filtration, I use less-costly hang-on-back filters like Aquaclears (biggest I can afford). They do great at moving the surface of the water as well.