Hi
Just to say that I have had Zwartbles and Shetlands and they are both lovely breeds but have learned over the years that there are lots of points to take into consideration - many of which you only learn with experience.
Zwartbles are very hansome and very friendly but they are big and heavy and ours were prone to foot problems, and that is why we stopped keeping them.
Shetlands are much smaller and easier to handle and ours are also very friendly but they are very goat like and eat leaves, strip bark and so can do damage if there are trees in their field.
My advice is as a newcomer get sheep from a small hobby breeder who bucket trains their flock and insisit on friendly ones. It will make your life as novice shepherds a lot easier and more enjoyable.