Hey guys! Please help!

Basically i want to get my mount/companion chocobo.

I understand that you need to join a grand company first. When and how?

I'm at my lvl 19 class quests. I was just ambushed in uldah area...and now about to fight ifrit (assuming duty finder works tonight when i get off work)

How much further into my class quests do i gotta go until i can join a grand company? Or is it unrelated and i just need to go some place else?

Also...what lvl can i use my chocobo in combat?