I think we can all agree that the Duggars have too many kids, at 19. In the largely Irish Catholic town I grew up in, there were families with 8, 10 or even 12 kids. Not common, but enough. I'm one of four. Not huge by historical standards, but a "big" family by current standards. Even though most people I knew growing up were one of three or four kids in a family.
So, how many kids is "too many"? I think it has to be judged by a case by case for sure. I have three, and I'm overwhelmed at times. And, to be honest, I was completely overwhelmed for six of seven the years that my youngest has been alive. My husband is very helpful, but he works 60-80+ hours a week (he's a chef). I work 40 hours a week (staying home is not an option for me for mental health reasons- I am not cut out to be a stay-at-home Mom). When I'm "home" I'm actually running around trying to get everything else done. Money isn't the problem as much as time- there's just not enough time in a week to complete everything, at least in my world. Another kid at this point would tip me over the edge completely. I'm just now seeing the light at the end of the tunnel. The day to day minutia of raising little kids completely burns me out (and I hated it a LOT of the time). Now that I can have some free time, grocery shop alone, and not have to watch the kids as closely, I'm staring to take a lot better care of myself. I don't regret any of my kids, but I do think, looking back, that I (we) really should have stopped at two.