One power supply can power both strands through the two output controller. Just get one that can handle 6 amps like the one I linked.
As an aside, they also make controllers with up to five outputs to run five separate strands.
I used Rosco super saturated black velour and love it. Wouldn't want to change anything. My ceiling is a black hole. the corners literally disappear. I used a sprayer, not a roller.
It is completely black with no reflections at all. The only time it doesn't look completely black is when I take a 500 watt halogen work light and shine it directly on the ceiling from a few feet away - that gives it a bit of a gray look. You obviously wouldn't be doing that while watching a movie. Since you dilute it 1:1 with water, one gallon makes two. Just make sure to mix it really well or it will be thicker towards the bottom. I mixed a quart at a time to make it easier.
Rosco says that it is a minimum of 1:1. Others have tried to go with more paint/less water thinking it would have better coverage, but discovered it wasn't as "black".
You can find some great deals on sprayers. I bought a fantastic reconditioned HVLP sprayer for $50. They were out of the one I ordered (Graco Hv2900), so they sent me the next model up (HV3900). Here is one for $66, but you can find them for less:
I even used mine to spray all of my stain and clear in my theater. The thing does a fantastic job. I have used it several times now. It has definitely paid for itself.