I'd go with the trailer, which you could likely find used on CL and then resell when no longer needed. Then you don't need to worry about which bike you are using. Get what is comfortable and safe for you, as you aren't going to be setting any land speed records in the coming years. From your description, sounds like you are riding the CCT for part of your commute, and then city streets. I'd be really nervous hauling a baby on DC streets, but maybe it's not that bad where you plan to ride. One of those flag thingies on the trailer would be useful for cars to see you better.