That is enough height to work with the 400 HPS. Absolutely better choice than the cfls, assuming you can control your temps. HID's get hot. Move your ballast out of your grow room if possible. Keep all wires off the floor, electricity and water dont mix very well, atleast in your favor
Veg time is going to be dependent on many factors unique to your room. The cfls will give you a slower veg speed and thus require more time than say a MH. Digital ballasts can power both bulbs. Some magnetics can as well. If youre starting from seed then youre going to be veg'in for atleast 3 weeks. I go even longer when I am starting from clones, but our gardens are different. Next cycle run clones if you can. Cuts veg time down and you know exactly what youre in for stretch, yield, even color traits, which most of these things influence your question about veg time. If I was growing my sativa in your scenario, its veg and screen fill time is very different than my kush indica.
Yeah thats the right track. Its really whatever works for you. I top my plants in veg without a screen and then they get moved into a flower room and tied into a screen using
plant velcro. Really cheap and really convenient.
Youre welcome