You can also use acetone to wipe it down before paint...but brake cleaner is prob easier. Rustoleum makes good spray paint for metal. Just a tip, after a few coats of primer, I would let it dry for a couple days. Keep it in a dry area with minimal dust during this process. After that, hit it was several coats of whatever color you want and, again, give it a couple days to dry. I didn't wait long enough when painting my rims and it didn't come out as nicely. My savage sliders, I was a bit more patient and paint came out much better.
Also, I noticed that when the spray can gets low, the paint comes out a little splotchy. I would only use down to about 3/4 of the can when spraying surfaces that can be seen. The parts that can't be seen as easily, go ahead and finish off the can.
Just my .02. And congrats on the bumpers! Extremely jealous.