I'll jump in here. I built a facility with 116 garages. Many of our units have 12' wide doors and all are 14' tall. While 12' seems reasonable, the vast majority would prefer 14' widths. By the time you account for mirrors and awnings, that 12' width shrinks quickly. Especially if you don't have a straight path into the garage.
From the standpoint of resale, don't build it any less than 50' depth. Those that can afford garages of this type, typically have 45' coaches. In reality, a 45' coach is more like 46'+ when you add bumpers, ladders etc.
I have 107 doors in my storage facility. All 14' tall. No issues with clearance as in California, the vehicle max height is 13'6"
If the door is balanced properly, any door opener will be just fine so long as it travels 14'.