Alot of people skip the skimmer on smaller tanks, it's not a bad thing to have but if you the water changes like you say then I bet you'll be fine. I didn't realize you needed an in sump skimmer, they are actually a bit more $$. And the nano skimmers in my opinion arent worth the money or hassle of trying to get it to work.
Pretty neat, that you have a sump for a small tank, that should give you some added stability as well. And a refugium is a great thing to have, very healthy and will help to keep your parameters in check.