It'll work for now. You know that you need a skimmer - so save your pennies. You know that you'll need RO water - so buy it at Wal-mart for now and save some more pennies.
I'd look into a HOB refugium if I was you. Aquatraders makes some nice HOB refugiums with a built in skimmer. That will take care of all your filtration needs and it has the skimmer too.
Small:
http://shop.aquatraders.com/Hang-On-Refugium-with-Protein-Skimmer-14in-p/43016.htm
Dump enough sand in the bottom to fill it up to the top of the baffle - usually about 6" deep. It'll take about 12lbs of sand to fill the small one up. I used this one on a couple tanks over the years. They work great. You'll need to supply your own powerhead. A Maxi-Jet 1200 works good, but if you can afford it a needle wheel pump would probably make the skimmer work a lot better.
Large:
http://shop.aquatraders.com/Hang-On-Refugium-with-Protein-Skimmer-24in-p/43017.htm
I never used the big one, but I do have a similar sized large HOB refugium from CPR and it took about 17lbs of sand to fill it up to the top of the baffle.
The HOB type filters with the mesh cartridges kinda suck. It'll work, but you will have to be very good about cleaning it every 3 or 4 days. If you slack off on cleaning it will start producing tons of nitrates and then your tank will be a disaster. When you do a water change, take the cartridge out of the HOB filter and rinse it in the old water before you dump it down the drain. It's messy, but by using that old tank water top clean your mesh cartridge - you will save any bacteria living on the mesh and you'll get rid of the sludge and gunk at the same time.
If you simply took that cartridge out and rinsed it in tap water - you will kill all the beneficial bacteria on it. Don't do that. Rinse it in old tank water.
Most of those cartridge filters have carbon inside the mesh bag. Buy a big huge container of carbon and replace the carbon in your mesh cartridge weekly when you do the water changes and rinse the mesh. It takes about 1/2 cup of carbon to refill those mesh bags - so a big jug of carbon for $20 should last you about a year.
I buy this 3.65L activated carbon:
Aquarium Filtration & Water Quality: Marineland Diamond Chemical Filtration Media
Your lights are kinda low on the wattage. You don't even have 2 watts per gallon of water yet. Look for a used clamp-on metal halide. I would look into adding some more light in the very near future. Mushrooms might do okay under 48w in a 28g tank if you keep them up in the middle of the tank, but I don't think they would survive on the bottom of the tank unless it's a very shallow tank.
It'll work, but you are going to need to do some upgrades in the first 6 months. Just go slow. Don't get more than 2 fish so your bio load stays low. I'd get an assortment of snails and crabs for your clean-up crew (CUC). Maybe 1 or 2 small turbo snails. About 10 astrea snails. Maybe 5 or 10 cerith snails. If you have more than 1" of sand in the tank get 2 or 3 nessarius snails. I'd go with red leg hermits and blue legs. Get about 15 crabs total.
Cycle it with a raw shrimp from the grocery store deli or you can just drop about 1/2 cube of frozen food in there. Wait 6-8 weeks and test it. When your ammonia and nitrites are both ZERO - check for nitrates. If nitrates are under 10ppm you're fine. If over 10ppm do a 50% water change and let it sit another week.
Don't cycle it with fish and be patient. Nothing
good happens fast in a reef tank. Only bad things happen fast in reefing.
Good luck and post some pics soon!!
