depending on what kinds or corals you want to keep it can vary. If you just want softies leathers and such, 3wts a gallon of PC can be enough, but if you want hard corals like LPS SPS you need MHs. Ive never dealt with LPS and SPS corals much but you need 6-7wts minium for those, Im not 100% sure on that.
As for a sump, what are you wanting to do with one? Just for more water volume and a place to put your heaters and other equipment. Or do you want an insump skimmer and a refugium. Ive build lots of sumps for myself and friends so get back with what you want to do.
If you just want a place to have extra water, and hide equipment, then you can make a sump very easy. Just put in an overflow box, if your tank isn't already drilled, have the water from the overflow go to a smaller tank, or rubbermaid tub below your main tank. Then have a pump that pumps less water then the overflow can handle bring water back into the tank. You can use PVC or soft plastic pipe.
hmm i looked at a few overflow boxes and they all were designed to go in the corner and had pumps that looked like they were meant for tanks with holes drilled in them. im gonna do some more research, thanks
ive also got another question, this whole water change means topping off evaporated water, or actualy taking water out and putting in new water? can someone please explain the difference if there is one.
topping off is when you add RO water to bring your water level back up. This is after evaporation. As you water evaporates you salinity level will increase. Adding water keeps you salinity stable.
Water changing is when you pump out, siphon out, cup out (however you choose to do it) a percentage of your tank water and replace it with salt/RO water mixed. This helps to keep your ammonia, nitrites, and nitrates down.
Also make sure you keep you salinity the same.