"I'm going for joint 50/50 for the next year until he starts school..."
When my folks divorced, the custody was 50/50. My parents did something rather unusual: They bought houses across the street from each other, and I switched houses every other day. (Eventually, it drifted to both houses several times a day, going wherever I wanted whenever I wanted.) It worked well.
I don't know whether this is feasible in your situation, but if it is, it's worth considering, to minimize the impact of divorce and custody issues on your son.