Hi Patti!
Well, the good news is that all of the runDisney races have a lot of new runners, so you will be in good company!! I think the festive and fun atmosphere really attracts those that are new to the sport, because it makes them feel comfortable. Of course, it's also a great excuse to go to Disney!!
My favorite race is the Wine and Dine Half Marathon that runs in November. The Princess Half Marathon is a great race to do with girlfriends, though! There are 5K races during all race weekends, and several are also offering 10K races, as well.
My advice is to pick what distance you want to conquer and go from there! You will also want to account for what race works best with your schedule, and if you prefer a morning or night race with an after-party. (The Tower of Terror 10-Miler and Wine and Dine Half Marathon are both night races with parties)
There is a schedule of race weekends with details about which race distances are available during each weekend on the
runDisney website.
You can book your actual trip any way you like! A lot of DVC members use their points for their race weekends. You will just register for the race through runDisney's registration link that can be found on the website.
I hope this helps! Please let me know if you have any other questions.