THG means to say that you need 3000/5000 lumens per square foot. The 2×4 tent you are talking about is 8 sq ft, so 40000 lumens minimum in flower. If you had a 8 bulb 48" t5 ho that is exactly 40000 lumens....that being said you will definitely want to scrog due to the penetration limits of t5 lights.You are still talking about 8 sq ft. Yes, you can use T5s--you will need more, as the 2 54W and the 2 39W are still not going to be nearly enough. You want a minimum of 3000 lumens for vegging and 5000 for flowering....and these are minimums, most of us run a lot more for flowering. While you do not need to go with as many as JAAM is running, you are going to need at least 6 54W 5000 lumen bulbs to veg and 8 to flower. I am helping a friend set up a grow and we are going with a 600W MH/HPS in a 2 x 4 tent.
I love having 2 tents and running a perpetual harvest. However, you mentioned that you had very little room. Do you have time, money, and space for another tent?
I would think almost any strain can be grown like that, I am running random freebies atm and the screen is maybe 5 inches above dirt level.I saw a grow one time where a guy used T5HO to go from veg to harvest. He had a set of shelves that he had built to go in a room where he didn't have a lot of space. these shelves were about 2.5' deep by 4' long and had 3 levels. The way he grew was to have the plants spread out in a very shallow scrog setup with the plants in RW cubes in small flood trays full of hydroton. If his plants were allowed to grow up, they would have been 3' tall, but he kept them growing out, beneath his screen which was 10" ffrom the surface of the medium.
He was able to keep the plants no taller than 10" with the scrog and the T5s were only another 1' above the screen so that when his buds grew through, they grew right up to the lights. He had his hydro tank reservoir on the floor beneath the lowest shelf so that the trays above just drained back into the tank after flooding. It worked quite well for him. Not the biggest, tightest nugs but solid quality and quantity buds none-the-less.
For someone with tight space to grow in, it did produce nicely, but I would imagine it would have to be only a certain few strains that could be grown this way.