1) If you talk as much as you say, about 3-4 of the $100 cards should be fine. The $10-$25 cards can be a rip off.
2) They do last a year, unless you buy a new card, then the time you activate those will be the new 365 expiration date and your other minutes roll over too.
3) You can either get their cheap phones that are probably going to be discontinued a month after you buy them (happened to me twice), or you can buy an unlocked phone and put one of their sim cards in it (what I'm doing now). Their phones are also cheap in the way that they are finicky as hell and won't pick up signals if you're more than a few hundred feet away from a tower.
4) You get phone service,voice mail, EXPENSIVE downloadable crap, and text messages only. No email, no sending pictures, no using websites to get around their restrictions, and you can't even use the text messages to communicate with automated services. There is no web surfing, just a couple of sites they have a contract with (CNN, SI, etc). It'll be fine if you don't use bells and whistles. I find it frustrating as hell, but it's all I can afford.