Scopists are here to make your life easier. There are good scopists out there and bad.
Scopists see all sorts of writers. Don't worry if your transcript is horrible, unless it is horrible on a consistent basis. Then worry. But seriously, scopists are not here to judge how good or bad a writer you are. If you are a truly horrible writer, they will either refuse to take work from you or charge you an arm an a leg.
I don't care what they say. Everyone has drops, except for maybe Mark K. (you know who I mean.)
Don't think your transcript has to be perfect before you send it to the scopist. That would kind of defeat the purpose of having a scopist. Then you need a proofer.
When should you start looking for a scopist? Well, I didn't use one my first year. I was learning my software, learning how to put out a good transcript. I was spending time getting a really good grasp of the mechanics of producing a transcript. I probably didn't get a scopist until my second or third year as a reporter. If you don't have a firm grasp of how you want something to look or your "own" style in producing transcripts, it's hard to answer someone else's questions.
Part II - scopists will be about where, when, and how.