Thanks everyone, this is very useful and great to get lots of different perspectives on things. Love the pics of the Shetlands and Castlemilks!
We want a small and easy-to-do sheep anyway, and definitely a native/rare breed, so we don't need a larger breed. There's just the two of us with extra for family and friends so these small breeds should be just right. We also want to mature them longer for better flavour and so we can make best use of the rayburn with slow cooking.
Have already found our local abattoir which is not far (as the OH also wants pigs but that's another story).
Andrew, if we decide on the shetlands I'll pm you regarding the wethers and taking a look, thanks for the offer.