You can start doing your research, and even interviewing midwives, before you reach that 8-12 week mark. They should be willing to meet with you and discuss their birth philosophy, their experience and how things work in their practice. Definitely don't feel like you have to go with the first one you meet - make sure you're happy, comfortable and compatible with your midwife. You'll be seeing them for a while!
(who is sticking with the same midwife we used last time, and can't wait to call her and tell her the good news!)