And you can normally travel at any level, but if you're in Limsa, you have to wait until you can access the airship, because the ferry is currently down.
If you started in Ul'dah or Grid you can freely move between those two.
Also, I agree with Tenchi that I'm sure they'll get everything sorted out before launch. The game itself is fine, it's just all the new stuff they're testing-- as he said, they got the data they needed.