1) I would say leveling is really quick actually compared to other MMOs I've played. Very little downtime at all if you don't want there to be
2) Yes
3) Absolutely. All class quests are designed to be done solo. You'll miss out on some heroic quests and flashpoints, but you can definitely skip those without an issue. There's more quests to do than you'll need to get to the next planet
4) I haven't seen any class that's terrible at soloing, but I've had friends tell me that the Sith Assassin/Jedi Shadow seem to be very underpowered.
5) This will depend a lot on class. My Juggernaut is fairly simple, but I know Agents tend to have a more complex rotation.
6) If you figure this one out, let me know. I'm broke.