I think that all hps need ballasts... along with all flurs... cfl's have the ballast built into the unit... there was some speculation on the board the other day about a hps bulb that had a built in ballast.. but nobody can get their hands on one... so it may just be a DREAM... lol

If you can ventilate and keep room temp at sutiable levels then go with the 150... the 250 ballast will probablynot work for the 150 bulb.... you will need a new ballast...

Ideal temp is 70-75.. but it is possible to grow in 85-90.... and a dedicated grower can do it.. you sound pretty dedicated..

: )