Is On To Richmond a good place to start if I've never played GCACW?
I have not played On To Richmond so I can't comment one way or the other. However, I will say that I've read and heard from a few people that the latest game in the series, Hood Strikes North, is a good way to get into the series as it is a single map game with only 2 counter sheets I believe. That being said there are a limit on the number of scenarios. When I first got into the system I took the advice of several people to get Roads to Gettysburg II as the amount of content in one box was the best bang for the buck.