Hi Rok - I will now try to answer that third question, about orchestral vacancies, turnover, etc.
This depends a great deal on the level of orchestra. if it is what I called a "destination" orchestra, like the Chicago Symphony and the like, then once one got a job in one of those, you would never leave, until you retired, unless you happened to win a position in another equivalent one. Or say you had a section job in one, but wanted to be a principal player somewhere. That is the only reason one might make a step down the ladder. These orchestras have the fewest openings, so it is a big deal when they do, especially in sections with not very many people (woodwinds, brass, percussion). String sections have more openings, simply because there are many more people in them. So even the very largest and best orchestras still usually have at least one string opening per season. But there may be literally decades between one say principal oboe opening and the next time there is one in that same orchestra.
At the other end of the spectrum, the "gig" orchestra made up of local free-lancers, turnover can be very high. They always have several openings each season.
For those third or fourth tier orchestras, such as say Charleston, or Knoxville, or places like that, they will have more openings than the larger orchestras do, but still much fewer than a "gig" orchestra that only does six or eight concert sets in a year.
So a musician can almost never wait for an opening in an orchestra he/she really wants to be in. There may never be one in his/her audition lifetime! In general, aspiring orchestral musicians don't get to pick where they live - they have to go take the auditions where the openings are.
When an orchestra has an opening, they advertise it in the musician's union paper (and nowadays usually on their website as well). Applicants send in resumes, and the audition committee goes over them, accepting some and rejecting most. Or they may have some candidates make preliminary recordings first, to help judge whether it will be worth their time to hear them. It is very difficult just to get an invitation to some of the very biggest orchestras - often, you already have to have a full time job playing in some other orchestra before they will give you the time of day. Other orchestras, though, including a couple of the very biggest, will have what we call "cattle call" auditions - they will let almost anyone show up. It just depends on the audition committee of the orchestra in question. Basically, the only other profession as difficult and competitive, or more, to actually get a good job in would be professional athletics, or acting. And we don't get paid nearly as much as the athletes do, even though we are just as talented, and in fact use much weaker muscle groups that have to last for much longer careers.
I realize that this post may bring up many more questions than it already answered - if so, I would be happy to elaborate. But I think it does answer your basic question.