1.) Yes, they are 5 minute phases, and no, there are no pauses. Pausing a live game usually kills it.

2.) Potentially. Some live games involve press, and those are very difficult in my opinion. They're a fun challenge once you know what you're doing. Most live games are gunboat, meaning there's no press at all, but they still move quickly enough that they require your absolute attention.

3.) Typically about 1.5-3 hours if you're surviving to the end, though I've had some that went over 5 hours. I would block out about 3 though.

Also, there is a little bit of etiquette that many new players miss. First and absolutely foremost, quitting a live game is not good. Don't leave the game even if things get bad. If something comes up and you absolutely have to go, try to find someone to sit your account and play the game out for you instead of just leaving. Secondly, if someone else quits, most players will elect to cancel or draw because games get unfair pretty quickly when a player leaves. There are some exceptions to that, but in my opinion, not all that many.