Hey,
I'm quite new to this too but I have researched my A$$ off and used all that knowledge in my present grow.

Could you tell us the wattage of each T5 bulb ? I'm guessing 45watts.

That gives you a 4 x 45w = 180w florescent grow. I would take the plastic cover off. But that's just me. I'm unsure if the plastic will subtract lumen.

Leaving the lights on 12/12 will only confuse the plants hormonally. It's best to leave them on 18/6 for the entire veg stage.
You said you read somewhere that 12/12 is OK for seedlings ? Maybe, but to be safe go 18 on and 6 off.
The bulbs you are using are designed for the veg stage. 6500 kelvin.
For the bloom stage you can leave just one of the 4 veg tubes in and replace 3 or them with the 2700k (warm white).
At the last 3 weeks of bloom make all 4 tubes warm white (2700k)

During the veg stage keep the light close to the plants. but be careful you don't burn them. Watch the spacing between the nodes on the plant. (where you see 2 leaves and then the next 2 leaves). You want to keep the spacing at around an inch to and inch and a half between these nodes. The closer the light the shorter the nodes. When the light is too far away the plant begins to stretch towards it. You don't want too much stretch in a small space. So shoot for the 1 inch node space. DMC1878 was right hen he said try to grow mainly Indicia strains as they are shorter, bushier plants. Maybe keep the light at 8 inches and just watch what it begins to do. you want to stop the stretch and see the nodes develop. Your plant will be almost telling you how high it wants the light. Maybe start at 10 inches and see what happens. I would keep it as low as I could without burning them or heat stressing them. But fluorescents aren't very hot anyway. Let me now how you get on.

For your pot I would use a 2 gallon pot/bucket. This would be a good size for your grow. Re-pot at least a week before bloom so the plants settle in.
Be careful you don't over-water, but water thoroughly, and keep the pots in trays so you can remove the excess water. This removes the chance of root rot.
Move the top soil around gently with your fingers before a watering. This will let it water evenly. Just to break the seal that develops on the soil.

Keep the cabinet well vented (have a low in-take and a high out-take opening).
The heat from the lights will create air movement to replace the air. A fan will be necessary too to strengthen the stems. If they stretch too far they can literally fall over. Train the stems gently to begin with.

Something you might have to think about in the future will be odour control.

You can follow my grow here too. I have a few pointers you might like. I have 10 entries so far. Its on this site under: 'LED grow testing the Pro-Grow 260' in Indoor growing.

You can also see it here: LED LOGGER

I hope this helps.

Take care