Two acres sounds a lot, I know, but it really isn't.
Whereabouts is the land? 2 acres in Dorset is a different kettle of fish to 2 acres in the Cumbrian uplands.
All herd animals need company of other animals of their own species, so no, you cannot keep one on its own or with just sheep for company. The Welfare Code for cattle states that all cattle should have company of their own species and stage. (Ie., two youngsters together is ok, one cow with her calf is not ok.)
I think it unlikely you have enough ground to rear two youngsters to slaughter weight. As a rule of thumb, 1 acre per horse or cow if it's excellent ground, drains well, not in a very wet area. Otherwise 2 or 3 acres per horse or cow, and you may still need to bring them in over winter. They may be hardy enough for the weather, but their hooves will trash wet ground.
If I were you, I would find a local farmer with cattle who can put some youngsters on your plot to graze it off for you - if he puts 4 or 5 on, they'll eat it off in a month or less - and then get your sheep on. Depending on the breed you choose and the ground, 8-10 sheep would probably be plenty. Get store lambs to fatten, not breeding ewes, at least for the first year. (And if you do want to have a breeding flock, then remember to account for the lambs when planning your stocking levels. If you chose a slow-maturing breed, then 4 breeding ewes would mean carrying 10-12 animals over winter - which might be too much for the ground, depending on how wet it gets.)
Were you thinking of getting livestock on straight away, or waiting till spring? If you can find a local farmer who's willing to graze it off for you, be guided by his/her advice on timing.
On growing your own beef, I really think you need to have a barn and more land to think about that. You could maybe contemplate getting a couple of castrated male weaned calves from your local dairy farm and rearing them for 'rose veal' - but you'd need to plan it out, have them going away before the wet winter weather comes.
Have a read of the info on the site that Dan linked for you, and a think, and come back to ask some more questions