If the frame already has paint/corrosion protection not sure why you would need to apply primer. If it were bare metal, but would think the reason for primer would be simply to discourage rust in this critical area. Only a guess, but if Primer is suggested, maybe it provides a bit of surface roughness as compared to glossy paint. If primer is used, automotive primer?

As for the clips, not sure about the longer straight'ish items with the diamond-shaped holes, but the boxier, squarish clips, using the center hole, mount to short flanged-top studs that are spaced around the frame. They are Trim Clips used to secure the Stainless Steel (looks like Chrome) Edge Trim that covers the window frame channel.

I have seen special replacement trim clips that have their own studs of sorts, that have screws that cause a cylinder to expand when tightened and mount in holes drilled into the frame edge.