Welcome to the hobby!

There's a lot of questions contained, so I'll pick a couple to answer. First off, it sounds like you'll be fine taking care of the maintenance end of things. Pinball isn't necessarily easy, but the techs here at Pinside are some of the most helpful people i know. If you have a problem, you can rest assured someone (or several people) here can help. There's nothing on these games that can't be fixed with enough determination.

As far as first game, i personally would go with AFM. That game is everything awesome about pinball in one exceptionally streamlined package. The sound package, the wiggling martians, the big saucer, the humor--such an awesome game. I think a couple young boys would have a blast with it. Next I'd go with ToM. So many fun toys and different modes to play, and again, i think the kids will love it. Can't comment much on the other 2, but you've got good taste for sure.

Good luck moving forward, and be sure to come visit the tech forums if you run into any trouble!