I think you can do the full without any problem as long as you start training for it early enough. You don't want to train for just the half and then try to start your training up to the full because you won't have enough time to get all your mileage in before January. If you start training for the full in early fall and use the half as part of your training, you should be fine.
As for getting injured, I don't think the first year has anything to do with it. Most injuries are caused by overuse, and that can happen in any year of a person's running career. It's probably more likely in your first year of running because you're going from no miles to lots of miles. That said, as long as your training program has you raising your mileage slowly and moderately, has plenty of rest days and cut-back weeks, and incorporates cross training to strengthen the rest of your body, I wouldn't be overly concerned about injury.
