The difference between a coach and a bus (apart from the body and seating) is the gearing.
It is perfectly possible to build a 'bus' with coach gearing (double overdrive ratio gearbox or lower numerical axle ratio) using standard transmission options - ie no special parts other than spares if you need to rebuild the transmission.
The disadvantage would be running in lower gears in urban areas, but the advantage would be less stress on the engine on 'fast' parts of the route (and, probably lower fuel consumption).
Of course, the compromise would be when you need to transfer vehicles onto other routes which are either hilly or congested.
