The worst thing you can do Bloomer is to overstock. You might be able to squeeze quite a few sheep onto that acreage, but the pasture will soon get sheep-sick, worm concentrations will rise rapidly and they will only have grass in late spring and early summer. It's a real recipe for scrawny sheep.
Are you intending to buy in lambs and rear them to slaughter age? Or buy ewes and breed from them? What breed are you intending to keep - you can keep a few more of the small primitives on the same acreage as slightly fewer big breeds. Are you intending to make hay on part of the land to feed your animals through the winter - you need to shut up the hay field from late April until haymaking which up here is July or into August.
What's the soil and grass like? If it's acid and full of rush then you will manage to keep far fewer sheep on it than were you to have lush Cheshire grass.
Sometimes 6 ewes per acre is quoted, but up here that would be impossible without a massive input of bought hay and concentrates. Sometimes one ewe per acre is quoted, or even one per 10 acres of very poor hill land.
So the answer is - it depends
Perhaps the best way to answer your own question is to try 3 per acre and see how they get on over the course of a whole year, then reassess after that time and adjust your numbers up or down accordingly.
Sorry - that doesn't help you calculate if it's worth renting the land, does it?
Incidentally, you could double up with hens at no effect on your sheep stocking rate.