I'd look at the reef octopus classic 100 hang on the back protein skimmer. I've tried a lot of HOB skimmers and this is the best I've found. I have found that most of the hob skimmers aren't worth the money. The reef octopus costs a bit more than the coral vue 150 vs 119 but it is well worth it.
I think you have the basics. I would get some good quality test kits. Other than that it kind of depends on your ultimate goal. If you want coral you'll probably need to upgrade your lights.
You may consider an auto top off system to deal with evaporation. Evaporation affects the stability of the water salinity, more of an issue with a small tank. There are some very expensive systems out there. I use a very inexpensive system. I have a float valve (looks a bit like those in a toilet but small) that hangs on the side of a tank and adjusts up and down to the height you want the water to be. Mine cost about $15 on Amazon. Mine is gravity fed from a $6 rubber made clear bin that I keep full of RODI water. There was a lady hear who put hers in a cabinet she built and hung above the tank. This is the one thing that allows me to leave for a couple days. My big tank loses about 1-2 gallons a day and my 40 gallon about 2 quarts a day.