Patrick...
Go to
http://www.cooperstowndreamspark.com, there is a link on the home page for umpires.
As for the experience level, there were guys there who were: mostly LL/JR/SL, HS, mens leagues, College, minor leauges and independent pro league experience.
You should have your basics down. If you have good positioning, timing and you sound confident in your calls you'll have a good basis. They give a quick rundown on where they'd like you positioned.
Do some studying of 3 and 4 man mechanics if you haven't done them before because you will get a chance there.
Then when you go enjoy the umpiring experience of a life time (I have to qualify the umpiring part because otherwise my wife might kill me). You will grow more in that one week of umpiring than you might otherwise in 1 or 2 seasons easily.
You'll also make 10-30 new friends you intend to keep forever. (assuming Randy get's us that damn list of addresses ! )