Hmm, pots to get? You are going to want to find some square pots IMO that you could use up until you sex and get the 3 4 that you want. I would look at your local $1 store if you have one or Wally World for square bathroom garbage cans and drill about a dozen little holes in the bottom for good dranage. You could probably use them up intil sexing even though they would be a little tight and then once you sex you could transfer into a few 2 or 3 gallon pots to give the roots room it would only take one transfer and once those plants sat in those pots until flowering they would have such a tight root ball there wouldn't be a root mess like you are worried about. Wo, hold on I just remembered the dimintions of your shower, why do you think that you couldn't fit 6 10in pots in there? How long do you want to veg for? They should have enough room IMO to handle the crowdedness untill you sex.
With the lights you don't just want the T5, you want the T5 high out put. If they are too spendy just get a nice mess of the CFL's. Don't get the bulbs untill you know the color skeem you need for veg and flower. Check out the wattages they have and get back to us.
Adieu