The Australian Open is almost here. As part of our preview package for the year’s first Grand Slam, Matt Cronin offers his top men’s storylines headed in to the fortnight in Melbourne. For the top women’s stories, click here.Where does Roger Federer go from here? So what’s left to motivate him at the Australian Open? Two things will get the Swiss pumped up: to avenge his painful and tearful five-set defeat to his archrival Rafael Nadal in the 2009 final and to show the young likes of Juan Martin Del Potro, who took him down at the U.S. Open, that’s he not done yet. Is Rafael Nadal back at the level where he can repeat as champion? After he took two long and classic five-setters over Fernando Verdasco and Federer at last year’s Australian Open, it looked like Nadal was prepared to dominate the rest of the season. After all, from June 2008 through January 2009, he won the French Open on clay, Wimbledon on grass, and the Olympic gold medal and Aussie Open on hardcourts. But then in the spring, the Spaniard’s body began to break down and he hasn’t won a title since early May. Is Juan Martin…