In terms of skimmers without a sump, I'd recommend looking into the reef octopus. Make sure you get one that is higher than the tank you are running.
In terms of powerheads, in my 55 reef I have 2 koralia 750s, 1 koralia 550,1 koralia 1050, and a marineland piece of garbage something or other which is along the lines of a koralia 1050. The amount of flow that you want is basically determined by the type of corals that you want to keep. I keep mostly SPS
corals, so I need more flow. There are some LPS
in my tank that are doing well as well.