What a lovely inheritance!
If you want to collect and use the grass, then mow it with a mower. If you just want to shorten it to make it more palatable to the sheep, and to control weeds, then top it and leave the toppings - the sheep will eat them as they dry in situ.
How many sheep per acre depends on the type of grass / terrain, the climate and the type of sheep; hereabouts, severely disadvantaged in north Cumbria, 2 commercial type sheep /acre is plenty for reshy rough pasture. Maybe 3/acre in a good summer but not all year round. If you chose a primitive type, you could carry a few more.