Any other suggestions for how I could run this? Aim is to have two lambs per year for the freezer, and try to avoid costs and hassle as much as possible.
Buy four lambs now (just weaned and already vaccinated if you don't want hassle, or 'cade' orphans if you do!), and a big chest freezer.
Let them grow big, then put them all in the freezer. Then eat the meat out of the freezer until it's empty, rinse and repeat!
Alternatively, let the grazing to somebody and use the money to buy half lamb boxes from, er, me for instance!