Just About Ready for Clones

Looking for a little help on a few questions. I finished building 2 cabinets both are 4x2.5x5. I have t5's in one and 600 hps in the other. I put a 400cfm inline fan with speed controller and ran duct into both cabinets to exhaust the hood and heat. Should I bring in outside air? my cabinets are outside? If I only have 4 feet from pots to light how long/tall should I let them veg before flowering? will they double in size when they flower? First time indoor thanks for info. Pics coming soon

5 feet is barely enough room really.....you be better of growing short indica dominate strains and flower them at 12 inchs high id say..