Alright Chris, if the car will stay black (and I assume it will), then you'll need to feather out the edges first.
I would personally use 320 to do this. You'll want to keep your da flat while doing it. I'll need to post a picture of a properly feathered edge. I have one from when I was stripping my spoiler on doby. Look how the paint smoothly transitions from one layer of paint to the next.
You could use 180 even for this to get the edges to feather better, then sand around the area to about six inches away from the feathering. This area just provides the mechanical bonding area for the primer overspray.
Then mask around that area, and your car being black, I would cover the whole thing with a drop cloth or something like the plastic I use at work. Depending on the primer you use, it'll travel as overspray and stick on other areas of your car. Our primer (Sherwin Williams) stays open long enough to still stick on the other end of the car, others aren't so bad though, and it may not be a problem for you. But unless you feel like cleaning off overspray with a clay bar, just cover the whole thing.
The immediate masking area around where you sanded should be at the end of your sanded area. Do NOT spray the primer all of the way to the paper, you'll leave a hardline that will cause the underlying paint to swell and it will leave a line that you think you'll have blocked out later until you notice a week after you have painted the panel that there is a residual line there from the paint shrinking back as it dries.
So, spray the first coat just over the immediate feathered edge, the next just slightly farther, then one more slightly farther. Let it harden up for ten or fifteen minutes and remove your masking.
I would let this primer sit untouched for about a week if I were you. It will shrink back (harden and dry) during this period. If you don't allow this time, you'll probably see residual shrinking back scratches appear after you paint the car black again.
Once you've done this, let me know, we'll cover the prep and painting process then.