Try beginning your process here by checking out the resources listed in Development Resources -
http://www.orbiter-forum.com/showthread.php?t=715
Most of the programs listed here are free.
Several 3d modeling programs actually have converters now specifically for Orbiter as well so it'll be a process of finding which programs work best for you. Anim8or remains one of the simplest to learn I think, however is way more limited than Blender is (both have plugin converters for Orbiter).
Doing "drafts" with Vinka's Spacecraft3 and Multistage 2 is a good way to learn things, too. I learned way more by opening and studying addon developers Spacecraft3 .ini files than I ever did by reading the Orbiter SDK (except to kick myself a few times for giving up C when it went Turbo and ++ years ago). The nice thing about "drafting" your projects with SC3 is you can quickly make changes to your .ini files, save, and then fire up the current state in Orbiter to quickly see the changes you've made.
You'll find the developers here are mighty helpful for just about every step of your project's creation, too.
Good luck!