Thanks for all the replies, it has given me some things to think about. 

I am modeling a very small portion of the C&O at Quinnimont and Prince WV and the Piney Creek branchline up to Raleigh. My layout while 25x30 seems fairly large, I have opted to only model a section that is just 1 mile on the timetable. Doing so I have been able to model the yards at Quinnimont track for track. My focus will be on operations, but not your typical spotting cars at industries. Mine is based on mainline trains bringing empties hopper trains from staging to the yard at Quinnimont dropping them and returning with loads and branchline trains originating at Raleigh and bringing loads down to Quinnimont and returning with empties. The entire layout will only have 1 active tipple on the modeled section. The only other businesses are the freight houses at Quinnimont and Raleigh. 

I figure I will need about 400 cars for my layout with 75% of those being hoppers or high side coal gons. That leaves me with about 100 freight cars not intended for coal transport, of those I figure only half should be C&O. While I love a beautiful highly detailed model, it is not something that I feel is necessary for my layout. I am OK with cast on grabs, but not so much oversized door hardware. I feel that Accurail and Branchline Yardmaster style kits are the minimum that I will accept. 

So now looking at where is MY line for freight cars?

1. Sides have to be 90% correct. This means that the doors need to be the correct size and type, the number of panels or ribs on a gondola or hopper need to be correct. The lettering should also be quite accurate for the era I am modeling. 
2. The roof has to be of the correct basic type. When a car is on the layout, the roof is the second most visible part of the model. 
3. The car ends while important, are not really seen on the layout. These should still be close, I wouldn't want a PS end on a car that should have a dreadnaught on it. But if the model has a 4/4 end when It should have a 4/5 end. 
4. Underbody details, cut levers, air hoses, proto wheels & scale couplers have little to no interest to me. I just don't see them on a moving model train. 

I should also state the cars of my era, 1952 trumps everything else. I have gone over the ORER for the year I am modeling and used that as a guide and from there trying to figure out what is the best model to start off with to achieve my desired prototype.