Probably an overflow box inside the tank in the center. LED's can be as expensive as you let them be. I have done extensive research, and I haven't found an LED fixture that would fit my needs as well as fit in my budget. I have several SPS corals that need fairly strong lighting in the proper wavelengths, and to rig up my 6' tank with quality LED's that would meet those needs will easily set me back $1K+. I opted for the higher cost of operation, yet tried-and-true T5 HO lighting. I have less than $300 in my lighting, and that includes 6 top-of-the-line bulbs. There are lots of LED manufacturers out there that offer "full spectrum" lighting, but since QC isn't very strict on a lot of these manufacturers (can we say Chinese?), so there's no telling how much of each wavelength is actually usable by corals. If you want something just to add "visible light" to your tank, these are okay. I don't trust any of them... other than the premium fixtures from top manufacturers. Since they use the highest quality components in high-tech facilities, those come with a hefty price tag. I can replace a lot of bulbs for that kind of money. Just my 2c...
If the tank is going to be open on top, a rimless tank does have a much better look to it. If you plan to use a canopy, either type (rimmed or rimless) will suffice. Open or covered tanks are owner preferences. Both my tanks have canopies. I like them because they match the tank stand, and they cover the lights. Mine actually holds the lights. I think the best reason I like them is because it prevents light from spilling into the room. My wife and I prefer subdued lighting, especially in the evening when we're trying to relax and watch TV, and they definitely help. The glow from the tank is very tolerable...
