I’m coming to this thread late but I have a recently created herd of 4 sows.
I bonded a new pair of young piggies with my 2 older sows who had recently lost a cagemate.
Bonding was stressful but they settled happily.
I would echo everything said about bedding, cleaning, cost of feeding and vet bills.
However- watching the dynamics and relationships within a herd is worth it all.
Looking forward to hearing more about yours