Though I am not far from complete noob myself, I can answer a few of your questions.

1. My main started as a THM with the intentions of becoming a BLM but now I'm sure I want to become a SMN, is it still possible to make him a SMN? How so? (SMN is summoner, right? Lol)
Yes, you can. Just pick up the arcanist class and get that to level 30. The second requirement is thm level 15.

2. Is it possible to edit character appearance after character creation?
Apparently they will be putting this in game in a future update. It should include changing things like hairstyles, scars, and generally cosmetic features. Right now, if you subscribe for enough time, one of the bonuses is one bottle of fantasia, which allows you to change everything about your character (including gender and race, I believe), but leaves you with the same name.


3. Could one character assume every job in the game?
Yes. There's really no need to make other characters.

4. At what level do raids start to come in?
About level 17-20 iirc you start getting 4-man instances. If you follow the main story quests, you will get get to them.
5. Are 8 sets of hot bars necessary?

6. Is there a cap on how many characters can be created?
Depending on the subscription you choose, it is either 1 per server or 8 per server.

7. How long would it take one to become level 50? (I'm not in a hurry, just curious)
This depends so much on your play style and time that it is hard to say. I have heard of people who got to 50 in less than 2 weeks.

8. Which job is least common yet important?

9. Can 1 character assume every role? Dps, tank, healer, troll.
Yup! By switching class/jobs, which can be done by equiping the main hand weapon for the relevant class, and there is a nice system for equipment sets that allows you to switch all equips at the click of a button. Trolls are a special case though. Troll can be equipped while any class...including forum rat