Hi! Please don't go for more than a couple of boars living together - anything above is bound to end with fights and permanent fall outs as soon as the boars hit the big hormones - unless you have oodles and oodles of space so each boar can have his own territory of at least 1 square metre. If you want more piggies in one group, you have to go for sows (plus one neutered boar if you wish to - he's very good at keeping the peace and soaking up any quarrels).
I can also only urge you to go rescue - my shop piggy career promptly started (and ended) with a surprise pregnancy and all the attendant problems - and I am sadly not an exception; have a look in our pregnancy section! A good rescue will not only rehome only healthy, properly sexed and guaranteed not pregnant piggies, they will also support you during the settling in period.
If I were you, I'd start with an already bonded couple or trio and expand bit by bit. I would also mix ages; you get more stability within a group as they always have a clearly defined hierarchy and differentiated tasks.
Please don't underestimate the amount of work and the amount of space that a group of piggies will require. You also will need to treat all piggies in a group if you have health problems like mites or fungal and that can quickly push you to your limits, as well as be rather costly!
I have 16 piggies myself, 11 of them living currently in one big group with a neutered boar resembling a piggy core group in the wild with ages ranging from 3 years to 4 months old.
I can also recommend Windwhistle Warren warmly.