Firstly welcome to the forum, you'll find lots of friendly like minded people here and plenty of good advice.
You don't need to do your 6 games before you can start in the leagues, you can do league games as part of all of your 6.
Speak to various ref's sec's for the different leagues you want to ref in and let them know you're available. Certainly speak to more than one, until you get going and they get used to you you will only get odd games so spinning a few plates means you can end up with a game most of the time you want it.
The other advantage to doing a few leagues and keeping your options open means if you find you don't like a particular league for some reason you haven't put all your eggs in one basket.
Find out what leagues kick off when and approach the refs secs for the leagues that kick off at the times you are generally available most weeks.Remember you'll need to be there an hour before though.
Finally if you're insistent in getting through the 6 quickly do youth stuff that's say 20 mins one way (just make sure offside is in play or it won't count), and you can do two or 3 of those games in one day, so maybe two weeks.
I personally wouldn't recommend that though, take the 6 games as a real learning curve rather than something you just want to get done as soon as you can, no matter how tempting it may be.....