I would upgrade to 400 watt hps. If your plants are 8wks old and only a foot tall you can get away with 3 gallon pots, 5 gallon would be over kill and a waste of soil. You'll have to get more soil to fill the pot, try to upgrade to at the very least Scott's. Fill the new pots with soil leaving a hole big enough to fit the root ball you're about to remove from the old pot. Dampen the soil slightly before the swith and don't compact it too hard. Throw in a view drops of Superthrive with the water used to dampen and in the initial watering after the switch. Run a thin blade around the perimeter of the soil in the old pot so the root ball comes out easily. Hold the plant by it base, pick up the plant and gently tap down on the pot. OR pick it up at the base, flip it upside downand gently pull the pot upward. Loosen the root ball so it's not tight and compacted. Use you hand or run a blade vertically down the root ball about 1/2 inch deep. When the root ball is moved fill the pot absolutely all the way up to the brim. As you water the soil will naturally compress and sink down into the pot. Some say the surface of the soil in the old pot should be the surface in the new pot. I don't see what possible benefit that could have. I bury the stem up to 4 or 5 inches from the bottom leaves. Reduce you lighting for 2 or 3 days afterward, maybe a screen between the lights and plants or something. Lastly, transplant just before the lights go out for the night cycle, never 1st thing in the "morning"