Welcome to MAAST Saltier.

Ace (hobogato) builds sumps and all things acrylic. You have to ask him though.

I have a 75g, which is a 90 short

For a 90 these are the items that I would buy, without breaking the bank. Somethings you CANNOT skimp on, especially if you want to be successful. You must buy right the first time. Sometimes the LFS may or may not have the "best bang for the buck" so always do your research before making any large purchases.

Lighting:
I would go with either T5 or MH. Since you mention T5, I would buy a 6-8 bulb 54w T5 Retrofit Kit with icecap ballasts and individual reflectors. The individual reflectors will give you enough PAR (err... light...) to grow any corals you want. The more bulbs, the better. I say that because T5s can tend to show "color bands" where you can see distinct color changes from each individual bulb. The more you have, the more they blend. The key things here are icecap and Single Lamp Reflectors. www.hellolights.com www.reefgeek.com

Protein Skimmer
Get a Reef Octopus, one for a 90 will run maybe 150, you can buy these locally at this price.

RO/DI
You need one. Flat out. www.buckeyefieldsupply.com or air water and ice, can't remember their URL.

Sump.
You can do alot with a sump or fuge. I have a 29g that my overflow just drains into. It has about a 6-7" sandbed for dentrification, around 100 pounds of rock (wet), and the remainder of the space if filled with macro algae. I do not have any baffles, I just buried the return in a bunch of rubble that was big enough not to get sucked into the pump, then covered that with rubble. This way I do not need to clean a prefilter every other day. My sump is setup for denitrification since I am growing "sticks" (Small Polyp Stony) corals.

Heater
Buy one that is enclosed. Ask anyone here how much fun it is to have a heater burst. It simply is not fun.

Return Pump
NEVER OVERSIZE YOUR PUMP. The size of your return pump must be smaller than what your overflow can drain. ACCOUNT FOR A SLOW DRAIN. I think 1 1/2" drains run at 1200 gph, I have a Danner Mag 7 return pump (internal) with about 4' of head loss, so it probably pumps at a few hundred or so gph. If you get one that is fast, you will quickly overflow your tank, especially if a rogue snail makes it into your overflow and clogs things a bit.

Powerheads.
Koralia makes a fantastic product and you can find used ones all over the place. I would recommend placing your powerheads so your water flows in a circle, around your rocks. Keeping excess foods in suspension to be either eaten or filtered out is what you want. Food will quickly decay causing excessive buildup of nutrients and other nasties that will eventually drive you either crazy or right back to the for sale forum to sell your stuff.

Clean Up Crew.
Always have alot. I buy crabs and snails just about every other time I visit the LFS. This is a huge detriment to your tank as they eat food that needs to be eaten. They are scavengers, just what a good reef needs.

Livestock.
Check out www.liveaquaria.com
You can check fish by their biotope. Very cool.

Patience.
This is the key here. Let your system mature before you add anything. There is much more going on than you will ever see with the naked eye. Just let it sit there for a few months, let the microscopic organisms thrive in there, as to not be instantly disposed of when you start adding fish. The longer you wait, the better.