I've been driving commercial carriages (city, weddings, etc) for 7 years now and am finally breaking free to work for myself. In my years I have seen carriage horses work in both breast pull and full collar and hames type harnesses. I just wanted to hear a bit for the pros and cons on each, considering we will typically be hauling a 1000lb 4-wheel carriage (plus passenger weight). I also wonder how the weight of the collar and hames (that appears to be sitting on the horse's neck) would affect a horse that may spend most of an 8-hour shift standing, rather than pulling.
The horse I am planning on getting is a 7yo Shire mare, unbroke, so she will not have proper muscle development for the first few months, and from what I gather, even on a mature horse, the addition of muscle from work can make a collar no longer fit correctly, which would mean purchasing a second collar down the road.