I use the 8 bulb T5's for veg and they totally rock.
As far as flower just go for 1000w man. People talk about 600's being more efficient and what not but the bottom line after having quality buds will be yield. My buddy grows with 600's and brags about how he saves money on his bill. Meanwhile my 2 x 1000w set up yields an extra P every 70 days. But hey, he gets to save $75mo or whatever it is
Technically you can easily do 20 smaller plants in a 4x4 tray with a single 1000w over it. Or do it Al b fuct style and do a single 1000w in an Adjust A Wing hood over a 4x8. That sounds bitchen to me. 20 plants in a 4x8 is perfect.[
using 1000w dosent that produce more heat and when you blow it outside wouldnt it be easier for IR chopper to see it. it will be in the basement double insulated would i be able to harvest a big crop with 400w for 20 plants