We had seven when I was a kid too. Our neighbor passed away and left a note asking mom to take her dogs. Her kids were going to put them to sleep otherwise. Since we already knew the dogs and they got along with ours, we kept them. It was doable because we had an acre of land fenced in and everyone got along well. My siblings and I all love animals and were happy to pitch in. I couldn't take care of that many dogs on my own though. I believe the neighbor also left some money for their care, because I know they didn't break the budget.
I don't think there's a certain number that is too many. If a person can afford to take care of them and can give them time and attention, and the dogs get along well, then I say the more the merrier. That's not my reality though. I have one dog and three cats. That's about all I can handle. A litter of pups sounds like fun though.