Painting the pieces question

From my vague understanding, people have said the minis are difficult to paint because of the material they’re made out of: that primer won’t stick, or sticks too well, I really don’t remember what the complaints have been.

I learned painting minis on the Middle Earth Strategy Battle Game minis (plastic, metal, and resin), so that is the breadth of my experience with the hobby. I think I’m okay at it.

So I really, really want to paint my WotR minis, but keep reading these cautionary stories about doing so. Yet I also see peoples’ painted sets.

So my question is: I want to do this. What do I need to know? What problems should I expect?