I leave Brittania metal parts (a form of pewter) in white vinegar for 30 minutes or so, wash in tap water, dry, then only handle with tweezers or exam gloves. I paint with Vallejo Model Color and it sticks well. Haven’t used a primer so far.
Bottom line…clean and prime…many ways to do both. I have simply used soap and water on many parts and primed with standard acrylic primer modeling paint…nothing fancy or extreme. No problems with finish acrylic paint staying on even over time…
I "Blacken" the white metal parts, been doing this for years on tank individual link tracks. There are numerous model paint makers that provide this liquid, Ammo from MIG and VMS are 2 I have used. Also a product called "Blacken It" has good results. Then primer and paint. Just my $.02.