(1) The intervals in the Bingham plan are good; four days a week plus two days a week cross training are not. I feel like I've been run over by a Mack truck. I think I'll ramp back to three days a week of run/walking.
(2) I'll probably do three days of cross training (bike, rowing, and elliptical probably) and see if that helps. If not, I'll drop back to 2 cross training days and have 2 rest days.
(3) Depending on how (1) and (2) go, I may be reassessing my spring schedule. It seemed a little ambitious on paper to do a half by May, and that may prove to be doubly so in reality. Also, a very good friend of mine from church wants to step outside her comfort zone and complete a sprint duathlon in June; she wants me to do it with her and I can't think of a better way to spend a spring day.
(4) The other thing I'm realizing is that I probably need fewer races in the spring/summer/fall to keep me motivated. I've been exercising 3-4 times per week for almost a year now, and I think that's become a permanent habit. I don't think I'll need as much external motivation.
(5) Yes, I've been eating enough and hydrating well.