adamr
I got the same primer and paint as you did. I was impressed with the primer as it covers the area nicely and dries very quickly with a nice finish.
I was shocked at the price (I paid less than you did but I can't remember how much).
In the end, I didn't even bother sanding the second controller as I went to Buco for the goods and they didn't have anything other than 40 grit sandpaper.
I took some 400 grit paper to my SSD to get rid of the paint and get through to the aluminum and it worked very nicely. I've painted that and it's dry so I'll upload pictures of that. You really need to paint carefully, otherwise you get a crinkle effect. I learnt that with my first controller painting exercise. I need to sand it again.
It's really cool though that I have a working custom controller and it wasn't hard to do.