Welcome. My history is much like yours. I just started officiating last year (and love it). Played in HS and 20 some years later got into officiating. I fortunately was coerced by a good friend to start ( he has been an official for 20+ years) and have been using him as a mentor (even subbed on his varsity crew a few games). I would suggest finding someone like that, it will help immensely.
He directed me to
http://www.honigs.com as well, and I purchased from them. They were great to work with. I didn't buy a "package" but put together items based on his recommendation for my area (NE WI). Honigs even allowed me to return a few items and switch them.
I agree the definitions are Key, and the thing that scared me most was that for as much football I followed (NFL, NCAA, HS, etc.) I didn't know squat when it came to rules, terms, enforcement, mechanics, etc. But, with the rule book, official's guide, and case book in hand, I feel more comfortable this year (that should sufficiently set me up for a fall).
Additional things to do to get into the swing is to tag along with a crew to a few games and watch the crew operate from the sidelines. It helps you get a better perspecitive on what the officials are watching etc.
Good Luck!