It's good that you know it's gonna take a little bit of money to get into growing. $2500 is a nice round number to start off with.
I get so tired of the people that would like to start a grow with only a few hundred dollars, and want advice on how to setup a small budget grow op.
It's hard to give advice to people like that, because it takes money to grow.
First off, a 5X5X7 grow room sounds very nice. It shouldn't be that hard to grow 10 nice size plants in that grow room. If it was me, I'd grow 25 plants SOG style.
I'd get 2 - 600 watt cool tube lights.
You'll need 2 - 265 cfm blowers, one for inlet, the other for exhaust.
Also get 2 - wall fans on each side of the walls. 2 wall fans on each of the walls will keep air flow centered right above the plants, and it will keep your room cooler.
Adding CO2 is a must IMO. It definitely makes a huge difference. Your plants will grow 1/3 bigger and more dense.
A CO2 regulator, tank, and monitor will run you about $500-$700 depending on where you buy it. But if you'd like to see what a difference CO2 makes, grow one crop without it.
I don't know what kind of water you'll be using, Tap, distilled, or RO water.
Tap has too many impurities in it, and distilled can get awfully expensive and annoying having to pick it up all the time.
I'd get an RO system, there alot less money now, You can pick up a decent one at HD for about $150-$180. The filters last about a 1000 gallons. The filters will last you about 4-6 months.
Those are the big items I'd get, there's a ton of little shit you have to get like vent hosing, timers, surge protectors, etc. etc. but I'm sure you know all that.
But set aside at least $300-$500 for nutrient. What's the point of having a nice grow room if you don't use decent nutrient.
One last thing, you might want to use some kind of satin finish/gloss paint for your walls. You'll have to wash your walls from time to time, and flat paint doesn't wash very well.
Good Luck.