Not bad for a "non KK expert" Mandy
I would say a maximum of 2kg per day between 2 non-breeding adults, but you will need to adjust this for weather conditions (more when wet & cold) & amount of grazing/foraging/additional fruit & veg available.
Clear the ground - oh yes, especially the younger KKs. If you spread their feed on the ground they'll definately turn it over. They adore nettles & brambles especially & will dig down to get at the roots. Don't worry about sloping, hilly ground - mine lived in a 2 acre woods when we were up in Scotland.
There is a breed smaller than KKs - "Little Swedish Pigs", but I don't know of any registered breeders other than Wendy Scudamore at Bartonhill (apologies in advance if there is anyone else out there).
As Mandy says, there are nearly always "Micro/Pet/Disney/Mini/Teacup" pigs "free to a good home" & you could give a couple of pigs a lovely home - just be aware that they will be of, probably undeterminable, cross-breeding (often with KK or Potbellie in there somewhere) & pigs don't stop growing in size until they are 2 (or even 3 in "big breeds").
If you're going for "rescues" just make sure their teeth, feet & joints are ok, as many that have been kept as "pets" have been cooped-up & become obese
KK's live, on average, 12-15 years old. If you are thinking KKs have a look on the BKKPS website - it's full of useful information & there are sometimes adverts for rehoming/older animals for sale, as well as registered breeding stock & piglets.