There is a man near me who keeps about 200 shet x wh ewes which he grazes on old landfill sites. They are small (40/45kg ) ewes that are very low management ewes---he crosses them to a texel and I think they rear about 1.2 lambs a year with almost zero inputs
W Horns will lamb easily to just about any sire (I've kept 200 WH for many years) but if you wanted a nice carcase lamb I wouldn't use a Shetland as a tup---In an ideal world I would go for something a bit meatier. I have used a meatlink with good success but any terminal sire would do
But a loaned tup may be a lot cheaper than buying one