The return pump should be rated for more than your overflow, I put a ball valve in mine so I could fine tune the flow back to the tank. For example, my return is rated for 1200gph and my return pump is set at 1500gph. This is in a 125g tank btw.
As far as a skimmer I would get one rated for up to double your tank size, better to have more skimming than not enough. Plus the manufacturers always over rate their skimmers so thats an easy guideline to be on the safe side.