I just upgraded to 4 on road, wasn't very into racing due to boredom and financial limitations, but I find cross to be alot more fun (i am more motivated to train for this season) and so I have planned to do a whole bunch of cross races.
I am riding a Redline frame, because it was cheap and alot of people in the Pacific Northwest ride them and like them alot. For this season all the parts are coming from my road bike where possible - 4ZA carbon tubulars, a mix of Campy Record-Chorus-Centaur shifters and derailleurs, Shimano and Tekro brakes, Rival crank, and a mix of alloy cockpit pieces. Really, the only carbon that I will be using is on my Record shifters and the carbon wheels - the shifters because they are the only working pair i have now, and the wheels because they are so much lighter then my other two wheelsets.
For spares I am just going to use clinchers with generic offroad tires.