I'd think about a paddock or two for hay and probably put your sheep on it after it is cut.
I wouldn't. We're almost the same as you - 3 ponies, two cows (hopefully in calf), 20 sheep including this years lambs, going up to 12/13 breeding ewes on about 10 acres of grass. We've loads of grass this year but we'll have more stock next year.
To make hay, we either need to do it by hand (not going to happen) or invest in quite a lot of machinery (tractor, mower, tedder, baler) or try and get someone to do it for us. With only an acre or two, we'll be bottom of the contractor's list and will probably end up with poor hay. We've decided it's better to stock to summer capacity and buy hay - at least then we can buy good stuff.
Also, if you take hay off, you will probably have to apply fertiliser at some point.
Just my opinion though.