/\ and a nice rough finish gives the body filler something nice to adhere to.

My advice would be to stop at a local body repair supply store and ask an associate for what you need. It's pretty self explanatory. The flexible plastic body filler "appliers" make it easy to apply the filler, but you can use anything really. Go light on the hardener so you have more time to apply the filler smoothly. This will save you time spent on sanding.