We are in a similar situation, but it is only a 7 hour drive, not cross country, so we can still see each other every few months. It is hard to leave family and friends and go off to adventure somewhere new.
I recommend you all Skype each other, or video chat over Xbox 360 live or something... it will be a fun connection for all of you. Start a private family blog on blogger where you all can update pictures and stories.
Also, build a network of help once you get there. I would go ahead and start looking into infant groups, join a baby/momma yoga class, mops preschool group, things to get you and your preschooler into meeting like minded people. Support systems are so valuable, especially in new places where you are a stay at home mom.
Congrats and good luck! Focus on the positive :)