Shetlands are lovely. As well as giving you some very tasty low CLA meat, you get their fleece and you could get the skins tanned if you are eating any. They are small, easy to handle, sound as if they would do well on your less than lush grazing AND they come in all sorts of colours and patterns.
Yes, with Shetlands, if you lamb at the natural time of April, which seems appropriate for a primitive breed, then in order to have a fair sized carcass to make slaughter and butchery charges worthwhile you will have to overwinter them on grass and hay, then let them fatten on spring grass and send them off in July or August. For your extra trouble, you get a wonderfully flavoursome, slow reared meat animal.
Shetlands really do tend to lamb easily, perhaps not as reliably as Hebrideans, but don't require the high lambing input some breeds need.
We always recommend that you start off with three ewe lambs, so born in April and you acquire them in August at 4 months. Shetlands are not bred at one year ( they go to the tup 5 months before their 2nd birthday) so you have more than a year to learn about your sheep, get to know them and for them to get to know you. If you are still nervous of lambing, then Shetlands will come to no harm waiting another year to breed.
If you are desperate to have some sheep now, you could try to source wethers which will be 10 months at the moment, and raise them to slaughter in July/August, but that is not a cost effective way to go.
For information about Shetlands and breeders, go to the Shetland Sheep Society (not the one in Shetland) to enquire. Shetlands are no longer a rare breed, so there are many breeders to choose from in all areas of the UK.
As with all breeds of sheep, if you decide later that you don't like the breed, you just eat them