I'd go with some T5 lights. Twenty inches isn't too deep, the T5's will treat you well at a decent price-point.
Skimmer: Get as much as you can afford, or as big as you can fit in your sump.
Reef Controller: This will automate everything. I use a Neptune Apex Lite and love it. It controls my lights, auto top off, dosing pumps, heater, powerheads, etc, all while letting me control everything wirelessly with my iphone. It also sends me a text message and email if there are any problems. It's important to keep your tank as stable as possible and the controller really lets you do that.
RO/DI unit: Get a bulkreefsupply unit. Another critical piece of reefing.