1. It would depend on the virus. The oral exchange (normally through bodily fluids exchanged by putting saliva in the blood stream) is the most common theory, but it could also theoretically be water or air born, depending on the author. It's the most popular because it actually gives us a bit of a chance. If it can be transmitted by breathing the same air as zombies or drinking water contaminated by zombies (some theories are that they wander into bodies of water while pursuing humans due to their primitive one-mindedness) it would practically be game over.
2.) Once again it depends on the virus. I personally prefer alive seeing as the virus can simply shut down parts of the brain or control your actions, but some favor reincarnation brought on by the virus.
3a.) My favorite theory on it is that the virus reverts the brain to a feral state and makes it constantly feed to sustain the virus.
3b.) I wouldn't know. If I were to write a zombie story right now, it would be because all beings would rather eat fresh meat than rotting flesh, but they would eat other zombies if there was a lack of food.
4.) It would depend on the answer to 2.). To me, the logical answer would be that if it were alive and could function like a human, muscles would rip and heal like normal. If they were dead or if parts of the brain (besides feeding) was shut down then we wouldn't have the ability to release chemicals to heal the muscles and you'd eventually just fall to the floor and be unable to move (If you play DnD, look up what happens when your strength stat falls to 0).
5a.) It would depend on 2, 3, and 4 combined. If you're alive and hunger for humans, then you'd likely just have instinct and adrenaline take over coupled with a lack of concern for your body that can be found in sentient humans, and be like a Left 4 Dead zombie, so quite deadly. If you died and just revived parts of your brain, then you'd likely have ripped or otherwise impaired muscles and would shamble around like Dead Rising zombies ( the examples are just to give you a visual).
5b.) I've given a little thought to mutations brought on by the virus. I don't know how or if this is even possible, but the virus could bring on mutations in your cells (like how cancer is just constant mutation of your cells) and if that could change your DNA, you could change into the "specialist" zombies that you can find in some games. I don't give much credit to it though.
6a.) That depends on the answer to 3. If it's brought on by instinct, then you'd actively try to kill and eat humans (as they're the most plentiful food source) to sustain the virus. Theoretically you could eat anything a human could, but with all that action you'd be more likely to eat meat to get more carbs and protein.
6b.) It depends on if your body just wants to spread the virus or sustain it. If the only goal is to spread, then you could very well bite them to exchange saliva and spread the virus, and then just leave them alone. Of course, you'd have to eat something eventually, and chances are it'll be human, but I guess the humans could feed you. Unless you zombify them while they're doing it of course :P
I loved those questions. If you haven't noticed, I enjoy discussing zombie theories :)