It's really only a 3 man race for #1. Federer might win Wimby, but I doubt he'll win the FO or the USO. As a fallback, Federer could play more tournaments to gain points.
Nadal's going to have problems keeping all the clay points since 4 tournaments are grouped in consecutive weeks. Likely he'll skip Hamburg, but that will cost him 350 points. Otherwise if he does play Hamburg/Rome/Monte Carlo/Barcelona, he's conceding summer hardcourt to Federer and Djokovic.
Djokovic is a wild card. Still a bit inconsistent to contend for #1 imo. He'll need to improve on clay and indoor surfaces. Winning the Olympics is possible and he can certainly pick up points from indoor Masters (Madrid, Paris) and Master's Cup. Losing all those points from Miami hurt.
Federer is going to have a rough year anyway you look at it. Nadal can take #1 as he controls his own destiny and has been the most consistent of the big 3 this year. If only he doesn't run from summer hardcourts....