Veg Cab specifically?

Well, my veg room is 3' x 5' x 6'...so a little skinnier and shorter than yours. I use an ebb and flow system and that allows me to be pretty flexible with how many plants i have in there. i've had anywhere between 2 and 12 at a time. i'm most comfortable with 5 or 6 plants. so i think you'll be fine vegging 5 plants in that size room.

i use 3 sets of 4' T8 Fluorescent lights for vegging and i think they work great. they pull much less power than a MH although i bet you'll see some killer growth with the MH.

My overall advice would be to take it slow. I'm currently on my third grow. I started with dreams of a perpetual harvest every 4 weeks...although it's possible...for a first timer it's way too much work to keep up with all phases of plant life while learning the ropes. unless you are somehow a natural and nothing goes wrong. I started with 2 plants my first time and yielded an ounce total. it was amazing weed, but a disappointing yield (had to share half with a buddy).

until you get a few under your belt, it isn't easy. I watched the greenman I Grow Chronic video and thought it was just a brainless easy process...WRONG!!...

anyways. your room sounds good to me. good luck
skeet.