The instructions from the floor leveling compound I purchase from the big box store, says to apply their primer to the concrete slab via roller, let it dry and then apply the leveling compound. Apparently, this is suppose to help adhesion. I will not be able to know exactly where the primer will go, so some parts of the slab will have primer but no leveling compound on top of it. Will this be a problem when applying Bostiks Best?

shouldn't be.

No, it won't effect it.

It will make for a better bond.

Thanks guys!!! I appreciate the feedback very much!! I'll post pictures when I'm finished with the project.