Wouldnt get a Shetland tup for a crate that around here, not enough in the Scottish Borders.... but I guess you have a few more up where you are....
Mine are white too, have two registered breeding ewes (only one of them in lamb though), two unregistered (they have come down from Shetland and are bigger than the registered ones, hopefully both of them in lamb) and then 4 lambs for this years breeding. My tup came down from Shetland too, but again before I got him. He's registered, but I'll have to find a replacement for his daughters this year...
Have got some bigger cross ewes too, and find that TXl Shetland crosses make good lambers and are a reasonable size (= manageable).