[NATIVEVAMAN]

T 5 refers to th diameter of the bulb 5/8 and I believe T 6 is 3/4 while T12 is 1.5.
I know of no current use of T 6 bulbs in aquarium applications.That doesnt mean it cant be done.
I am not a great fan of metal halide because of the heat factor. I have a set of 175 watt 14k's that sound like a vw idleing in my living room. Yeah they are old lol.I also am setting up a 65 g tank and considered them for it, but when the choice is a nice new set of t 5 vho's or a chiller I am going to opt for the t 5. I dont see the need for 8 bulbs on a 65 g tank but its a matter of choice. with vho t 5 4 may be enough and 6 certainly is. With ho i think i would go for 6. Unless your tank is over 18 inch's wid I dont think 8 will fit.
For the fuge on my 65 g I am going to use a 40 g breeder tank for the sump and rubber maid container of 10 g for the fuge.I will have to build a slightly oversized stand for this and my auto top off to fit.My fuge will gravity fed from a t in the drain line from the over flow and will drain via gravity directly to the back of the return pump avoiding the loss of pods to the skimmer and othe things that will run in my sump like carbon and phosphate filters.
I do plan on having a uv steralizer. I also am going to have a deep sand bed (dsb).The continuous use of uv may be detrimental to a dsb so my use of uv will be restricted to a few hours a day maybe 2 or less.
The flow from the skimmer will go right back into the sump. Since there is little to no pressure comming out of the skimmer there isnt much else you can do.
My plan for the sump would be. About 1/2 of the left side of the sump will be for skimmers and other filters.the right half will be for 3 to 4 under over baffles to remove bubbles. These will be filled with live rock rubble. and the far right end will be the return pump.My return pump will not be in the water at all,its a heat issue.If my tank needs heat ill let a heater do it.There will be 3 small pumps in the sump with the skimmer for carbon,phosphate and uv, but there heat output will be less than 10 watts while the return pump could be as much as 100 watts.
I have no clue what your return pump might be.I just looked at the pump section of this site and found none with the #7 in it.
As for the computer fans, I am sure they wont be enough if you decide to go with metal halide.For 45$'s you can get the temp controlled ice cap fans and work your way down from there.Im not sure I would protect my investment with a computer fan,I dont see the cfm being very high on these.