I should add that while the Offensive Coordinator position is a big hire for Scott Frost because it will signal what direction that offensive scheme is going (staying similar or complete overhaul)...
The most important hire for Frost is easily the Offensive Line coach.
This position must be filled by someone who is equally a tremendous teacher as he is a stickler for technique.
The O-line is what greases the groove for the rest of the offense. If the line struggles the whole offense struggles. (See the last 4 years)