new to this scene so... How do you start a convo with one and bring up the subject of a PSE, GFE, etc with the girl?

where are you running into them?  I assume you mean dancing at a club-  do a search here or elsewhere and see if she available- or they usually sign autographs or something afterwards- ask discreetly if she is available for 1 on 1- apparently Lisa Ann takes offense at being asked but I would guess most would not be offended if asked discreetly even if the answer is no

It depends on who it is, and where you're meeting them, and a lot of other things.  

I had a good time with a PS once meeting her in a club where she was featuring.  I took a "private dance" with her in the club and while we were in the back room, I asked her if there was any chance of getting even more private and more intimate.  You can guess about the rest.

DON'T do it where there are lots of people around who can overhear.
DON'T be crude about it.  
DON'T press her if she says "no".

No one wants to be treated differently. Just be yourself and stay true no matter who it is. Timid men around out in a crowd. Relax, smile, laugh....be confident and energetic and you will be the life of the party.