I think my preference is:
HC: Urban Meyer
DC: Maybe a veteran NFL DC (Ron Rivera...).
Somebody that can run a Hybrid 4-3 & 3-4 would be great but it has to be fundamentally sound, not that mess Rob Ryan tried to run. The Pats run a hybrid but switch back and forth on their base over the years based on their roster and possibly on how offenses are trending. They changed their base 4-3 in the Super Bowl to counter the specifics of the Rams blocking scheme. They've gone back to more 3-4 this year on 1st downs and short yardage but other downs are a hybrid.
OC: Meyer's choice from the college ranks. If his preferred choices are not available I think Kellen Moore with an HC like Meyer can become a good OC. I'm near-100% certain that Moore will be a top OC someday, somewhere but he needed a better HC as a rookie OC.
OL Coach: An extremely critical hire unless the new OC (like Shannahan in SF) is a master of OL schemes (specifically the ZBS). Columbo is good at coaching individual technique but he played in a man blocking scheme and is now trying to coach the ZBS.
If a new Head Coach just takes over the existing coaching staff, then it will likely fail.