Actinics are up to you. You won't NEED them, but you may want them. If you use a good reflector (lumenarc III) you can cover the whole spread with just the 1 bulb.
As for the HQI vs. regular ballast, You will get a little better growth running the 20k's off of the HQI but you will be replacing the bulb more often. I've ran radiums, ushio, PFO, and XM off of the HQI and I was changing bulbs around the 8-9 month mark.
Look into the M135 pulse start ballast if you're worried about changing out your bulb too often. I run a 400w ushio 10k off of a PFO pulse start and the color/intensity is great.
The 20k/HQI combo is hard to beat for color though.
Whatever you do, don't skimp on the reflector.