First off, if that ceiling hasn't been previously painted, you may want to invest in a shower cap, 'cause that stuff is going to rain down on you.
When rolling a raw acoustic ceiling you need to remember to get it right on the first pass, as laying off will start pulling the styrofoam chunks off in---chunks. The foam rollers work, but if you use any pressure whatsoever that shower cap will be serving a second purpose.
a half inch nap will not hold enough paint to be practical, use at least a 3/4.
Expect a lot of debris. Spray if at all possible.