When looking for a coach, there are things to consider. But overall, for any coach (besides his position development rankings) there is something that is most important. That is motivation. A coach with high motivation ability can get the best out of his players/ He can raise Work Ethic rating (which might therefore help enrich development). Considering I call my own games 90% of the time, I could care less about gameplan; and also you can scout your opponent and figure out one of your own.
When hiring an OC, make sure at the least he has the best development in OL. The offense starts and ends with O-line. OL opens holes for the backs and gives QB time to throw the ball. It is better to have substandard QBs and RBs operating behind a great line than great skill players behind a shitty line.
On average, this is what I would try to get as an OC:
Good at OL dev.
Average at QB, RB, WR dev.
Of course, depending on what school you play as and what conference you are in you may be able to get better or worse. Right now I have an OC at OleMiss who is Good at developing everything.
Cornerbacks are at a premium on defenses. If a team is a primary running team, you may have to stack 7 or 8 to stop them. This is why it is essential to have a DC that can develop DBs well. Make sure your DC has his highest rating in CB development.