I booked Patricia LeJeune about 8 months in advance...right around the time we confirmed our Escape wedding with Disney.
I know many who have booked earlier than that...Wishes brides, for example, can confirm with Disney at 12 months, so they tend to book outside vendors sooner than Escape brides. I think it depends on when your wedding is... If you are getting married on Valentine's Day, for example, you probably have to book way further out than someone getting married on a Tuesday in early November.
As for picking your hair/make-up people.... reading the PJs of fellow Disney brides was extremely helpful. I don't have the luxury of a trial-run, so I'm relying on other people's pictures to see the work of the various companies. Beaute Speciale and Patricia LeJeune seem to be the big two... And I think it just comes down to personal style....how much make-up you normally wear or want to wear on your wedding day... how you like your eyes to look, etc. Both get great reviews on the Boards.