Well you asked a question about the weathering and then answered it. So the next step is to do it and from that you will learn.
As to the paint, it's already glossy. Actually too glossy for the final result but glossy enough to weather IMO. I'd weather right over that, I just wouldn't be using your products because that's not what I use for weathering personally ( not saying you shouldn't or can't, just that I don't)..