For your last point, if you get given a game you aren't comfortable with tell your appointments officer and they should be happy to move you to a lower game. Assuming of course it isn't already in the bottom division in which case they have little room for manoeuvre.
Almost all leagues in England, and CFAs / the FA, work on an available if not closed system, therefore if you tell them you are available on Saturdays and / or Sundays (or midweeks) and you haven't closed that date you are likely to get appointed to a game. The onus is absolutely on you to keep your non-availability up to data, or availability if they work on your opened rather than closed dates. At all levels of the game you will get grief if you regularly forget to close your unavailable dates and they subsequently have to replace you, and that grief will get worse the higher you go. Remember that these appointment officers are often volunteers with full time paid jobs, they are there to help you and the least you can do is keep your availability up to date.
Also think about the home clubs. I once appointed six different referees to a game over a five day period, the first five all kicked it back even though their dates were open. Every time the home club secretary had to confirm the game with the referee, she got fed up of it and asked me what was going on, and actions of the referees, or rather their inactions, made me look incompetent. It takes a minute to close a date, it takes a lot longer to appoint a referee to a game.