I kept Gloucester old spot and tamworth pigs for several years on my smallholding, and they produced the best pork I have ever eaten.
We always bought weaners in the early spring and slaughtered them in the winter.
Make sure you have a good solid trailer for transporting to abbatoir as pigs are VERY strong and will totally destroy anything lightweight or flimsy.
We ended up slaughtering our pigs onsite using a local knackerman, as we wanted less stress on the pigs and to collect the blood for black pudding (Can't do this if you go to abbatoir as it's illegal!!).
Be prepared for 'sausage making' day. Get all your tools/supplies/ingredients ready well in advance and make sure there is plenty of room in the freezer. When the split carcass arrives on the kitchen table, you better be ready to start! (Obviously a lot easier if you are using a butchery service, but nowhere near as much fun!).
Same rules apply for keeping any animal: Keep them dry, fed and watered and you won't go far wrong. Pigs get sunburnt like us, which is why they like wallowing in mud. Keep them cool in summer by starting a mud hole for them and fill with water. They'll do the rest! They love being sprayed with water when it's hot.
They like wallowing in mud, but hate wet bedding. Keep their sty dry, free from draughts and regularly change the straw (We built wooden floors into our pig huts and that helped keep it clean and dry a lot.). We used arched metal sheeting bolted together and screwed to a base of fence posts for their huts. Then we cut a piece of thick marine ply to fit one end and screwed that in. Make everything really solid, or they will just destroy it.
We added things like old tyres and big logs to their area as they love to play. Just be ready to remove the tyres if they start eating them, but our's never did.
We used electric fencing, which they need to be trained on initially so make sure you are ready for a few escapees to start with (Use a pig board to ferry them back).
We fed them on pig pellets and any vegetable/fruit/bread scraps. We used to pick up out of date stuff from local shops and practically fed them on nothing but apples in the autumn as everyone in the village used to give us all their windfalls.
Fresh water changed twice a day. The water container needs to be made of or encased in concrete or they will just flip it all day long. Pigs are as smart as dogs, and quickly learn new tricks and routines. They love nothing more than being scratched on the tummy or behind the ears (Seriously).
We kept pigs, chickens, ducks, geese etc., but pigs were my favourite. You can watch them all day long and were a joy to keep.
And they taste good
You'll have to do all the DEFRA triplicate forms and crap every time you move them and register your smallholding if not done already. Just check the DEFRA website for more info.
Best of luck
Pete