I think there are some things newer runners could learn from your plan, namely taking the time to work your times down in the shorter events before trying to tackle the beast. That said, my one concern is that you are only giving yourself one shot at your goal. What happens if it’s a bad day? What happens if you fall just short? Hopefully, you’re going in with the attitude that, if you don’t get it in that one chance, you can push the goal back a month and give yourself more of a chance. If not, I’d probably suggest two shots at the goal.