I've only got as far as reading a couple of how to keep pigs, but will sometime take the plunge and get a couple for the freezer. I know people who have done the same, as well as reading posts one here, it seems from this bit of research that if you break even and have a freezer full of pork you're doing ok. I would be inclined to think about other things you could do with your four acres. If it's well fenced, and has water and a field shelter, horsey people might pay you £7-10 a week per pony, times three ponies, over a year, you'll be looking at proper money. My mum does this, it almost pays for her horses keep and the lease. Although it's hassle as any dragging gates or broken fences or anything are her responsibility.
This year I had a go with chickens. I bought eggs, hatched and reared them and sold the pullets... I just broke even... And am now down £60 odd after buying wormer. I feel like this was pretty good going for year one! Best of luck to you!