Best practice is to hire a GM and let him decide who the coach is and the direction this is going. Excited for this change.
As for Bill, he'll want to chase Don's record so he should def wait to see the NFC playoffs play out...if Cowboys, Eagles, or another repeat playoff team get bounced early, expect some coaches to get fired and BB swoops in. They'd have the roster ready for him.
As for power and coaching, Chargers have vacancies for both roles so I can see why they're favored to land BB. They have the QB.