I've pushed Jim Harbaugh before, and remain a fan. I've curtailed thoughts of the next coach here, but have unfortunately had to consider it since October.
Harbaugh's name kicked into high gear once Andrew Luck's hype hit critical mass, but he's been a solid candidate for years. As with any coach transitioning from college, the support staff is critical, and finding coaches with pro backgrounds to go with the two years Harbaugh coached in the league becomes critical. It being a buddy system for all real purposes, who he knows becomes a matter of candidacy.
So, here are some coaches who have background with Harbaugh in the past:
Geep Chryst, TEs coach, Panthers - was OC with Chargers while Harbaugh played there. Was the league's first quality control coach, 1991-95 with the Bears while Harbaugh was there.
Ron Rivera - Chargers DC, was LB on 7 Bears teams with Harbaugh.
Jim Schwartz, Lions head coach - quality control with the Ravens, 1998.
Mike Singletary, 49ers head coach - obviously, played some ball for the Bears. Hall of Famer and former assistant head coach of the 49ers, but has never been a coordinator. Comes from a 3-4 background, which may work for Harbaugh (a recent convert thanks to Vic Fangio).
Dave McGinnis - LBs coach with the Titans, and former Cardinals head coach - was LBs coach with the Bears (and coached Ron Rivera). Was on staff with Chryst with the Bears as well, and unrelated to Harbaugh, the two coached together with the Cardinals.
Of those coaches, only Chryst would have some guarantee. He's already here, has a history with Harbaugh, and can fit in various positions.
Most of the others require release from their contracts, and in the situation of guys like McGinnis or Rivera, would have the option of continuing on with their current staff wherever their current head coach goes, or getting a head coaching job themselves (Rivera being the hottest hand currently).
Schwartz probably has another year in Detroit, but if not, would make a fine coordinator (and was one with Tennessee, another link to McGinnis).
Here are coaches Harbaugh's employed that stand a good chance of being in the pros:
Greg Roman, assistant head coach/running game coordinator - was a Carolina Panther third tier (quality control) coach for both Dom Capers and George Seifert (95-01).
David Shaw, offensive coordinator/RBs coach - has pro experience with the Raiders and Ravens as a QBs coach, and was with Harbaugh at the University of San Diego.
Vic Fangio - former Panthers DC now holds the job for Harbaugh.
Fangio has a rocky history having been fired by Carolina once, and is a 3-4 coach (which would cause a long transition). Harbaugh himself didn't have a 3-4 past as a coach, but watched Fangio turn a terrible defense into a good one.
Roman's vital to Harbaugh's operation. Whether or not he'd continue to call his own plays in the pros, Roman holds a lot of weight on offense and directs a vital running game. Naturally, the other half of the offensive coin for Stanford, with pro experience, would be a logical hire as well. Ideally, neither would be a coordinator, but if Harbaugh is calling plays himself, it may not matter.