With regard to selling the end product, you will do far better selling to the consumer (that eats it) rather than the butcher, as the butcher will usually try for a low price, so they can make maximum profit on it. However, if you can build up a clientele of people who want to buy locally produced, happy meat etc, then you can do ok from that, and maybe selling some young stock, and then doing something with the fleeces etc.
But to be very honest you will struggle to make a viable income off a 20 acres sheep farm.
Things like holiday lets, camping, yurt holidays, course fishing lake, etc etc will make you far more per acre I would think. That kind of thing a long with the other bits and bobs might do ok for you.
But to live off 20 acres of sheep, would be a struggle.