Hi and welcome. Contact Defra about the holding number. I suspect you'll need one of your own as you will be the keeper of the holding. The paperwork's not too bad for the number of livestock and livestock movements you're going to have so don't worry about it. For sheep, pigs or cattle, you'll need a herd / flock number from Animal Health.
I'd agree with the pig idea. We keep three weaners on 2 pens 30ft x 40 ft from April to October; one for us, two to go. By the following April, ina normal year, the pens are recovered for the new intake. Keeping animals that aren't going to be there all year ie fattening lambs or pigs, rather than breeding stock will give the land a rest and save you buying winter feed and putting up shelters, thus keeping costs, particularly capital costs, down.