I don't know why most seem to think Manning will coach in the NFL. IMO he wont even be a GM. He has stated more than a few times his family comes before football. I just don't see him taking a job that involves as much time as coaching or being a GM does. I think the closest thing coming to football Manning does would be in broadcasting.
Needs to retire. Doesn't need the money, doesn't need the acholades, doesn't need to build more stats or does he. He'll be another side show in a circus a la Farve if he hangs around. Retire while you're on top, you'r legacy has been cemented no need to pad up your stats.