The primer and finish coat manufacturer that you are using usually has recommended surface conditioner preference. Check with your coatings distributor to see what is recommended.

I've seen some rust converting products that actually leave a significant residue on parts. If you can get a hold of some Ospho, that stuff converts the rust and does not add any additional coating and was compatible with a primer I used, but that was decades ago.

These days, I sand everything down with 80 grit, straighten the panel as much as I can and then seal it with catalyzed high build primer in multiple thin coats allowing plenty of dry time between them. Thick coats shrink too much, and once-invisible sand scratches will show up a few weeks/months later.