I don't have a Red Sea tank, but I have a DIY 40g cube with a 40g sump/refugium.
I'd recommend getting any of the DC powered return pumps that have variable speeds and maybe even a feed mode. Get one rated with the top flow rate that is more than Red Sea recommends (for insurance and to cover head loss).
I've used a number of different skimmers over the years and they all work pretty much the same. I have a Coral Box from Reef Breeders and it works well. I especially like the fact that it has a variable delay for turning it on after I feed and a float switch and alarm for the collection cup so it shuts off if the cup fills to full.
Most skimmers are fairly sensitive to the water level in the sump, so an ATO would be a useful investment. I have one that uses an electric eye rather than a float. I had one with a float and it always collected slim and needed cleaning every couple of day!
I have a basic cheap heater. But I live in SW Florida and our house is 80 degrees about 10 months of the year so I very rarely need a heater. Get one that is completely waterproof and with an on/off thermostat. They are cheap so this isn't a place to save money. Buy a good one and you'll be ahead in the long run. Cheap ones fail and either don't heat the tank or stay on and over heat the tank!
