A 12v pump & IBC for water sounds ideal, assuming there's no access down to the stream for the sheep to get their own water. Unless the sheep are on dry food, or lactating, they won't drink hardly anything anyway.
No need for a shelter either, sheep are meant to live outside all year. Unless you're lambing, there's no need of a shelter.
And yes, June/July would be an ideal time to look for store lambs. There won't be many about before then anyway. The grass may be far too long for sheep grazing by then though, unless the previous owner is keeping it down.
There are sheep grazing it at the moment. I should be able to find someone to graze it - or as you say, I can offer it to the person who is grazing it now.
My plan with the water was to fit a float switch in the water trough connected to a battery and 12v pump. I can then set up a second trough which will be gravity fed from the first. It all depends on whether I find water when I dig out the well. Good to know that the IBC is also a viable option. There's no easy way down to the stream