Welcome to TGPF Rabbitdan. As you can probably tell many members on the forum take piggy rescue very seriously, hence your decision to purchase pigs has ruffled some feathers. With so many piggies in rescue/foster care it is understandable why members are so anti shop/farm bought animals. Not all pigs in rescues are old, in fact many are youngsters who have been born in care so you would not necessarily have to take on an older piggy.
In answer to your question 2 or 3, either can work if they are all girls, if you want boys then I would stick with 2. We currently have a group of 4 living together quite happily (neutered boar and his 3 wivesx)), the key is to provide as much space as you can. I have never personally experienced problems with 3 pigs and have always worked on the basis that if I have 3 and lose 1 at least the piggies left behind will still have a friend. The minimum recommended size for a pair of piggies is 4'x2' so for 3 I would opt for 5' or 6' accommodation. Have a look on line for hutches, you generally get a better choice of size, the Happy Hutch Company do a good selection, here's a link
http://www.happyhutch.co.uk/single-storey-rabbit-hutches.php. If they are to be housed indoors you can buy a ready made cage from a shop/on line, again go for the largest possible either a Ferplast 120 or one of the 150 cages now available, although these tend to be harder to find. Have a look on Zooplus, they currently have some cages on special offer
http://www.zooplus.co.uk/shop/small_pets/hutches_cages/rabbit_cage. Another option is to have a C&C cage (DIY job) the advantage is you can make the cage to fit the space you have available - have a look through some of the housing threads on the forum.
I do hope you will stick around, there is a wealth of information on the forum and some very knowledgeable members too. One thing I would stress if you do decide to go with the farm piggies is please double check the sex of the babies (again threads on here to show you how to do that) the last thing you want is to end up with lots more piggies than you bargained for! Boys should be removed from their mums/sisters at 3 weeks of age, so something else to bear in mind. This is another big plus of getting pigs through a reputable rescue, they will be properly sexed, health checked and you will have a life time of support.
Good luck with your decision.