As for agency vs independent it's a toss-up. Personally; I avoid agencies like the plague, conversely many guys have great luck with them.

  Not having a work # doesn't mean you're "screwed". It does mean however they/she will ask for some other form of verification. Keep in mind they are mostly trying to verify whether you are safe and not Law Enforcement(LE). Since you have no work # to give them just be understanding and co-operative with alternative forms of verification they may ask for.(your not the first self employed/retired/independently wealthy guy too call)  

  As for a highly experienced gal vs a relative newb? The experienced lady will more often be able to understand and deal with your neophyte nervousness. A less experienced gal although fresher and quite often less “pro” in demeanor may be put-off by your trepidation.

  Good luck, and I'll look forward to your first review  

In canada so the requirements of screening is much less than here. She would look at your passport or drivers license and may forgive the absence of work verification. I would email them before you get there to start your rapore.
tyvm,P.T.

I have used them before. They require some registration and most contact is by email. They provide you with a registration number so that only you can access their website or email them via the number. More complex than some agencies, but I was not deterred. Their women are typically young and match their pictures reasonably well. Many are young dancers or students. Your results may vary from ok to exceptional but all of the ones that I saw worked hard to please.