I say the more the merrier
I have a "few"
and they all get along awesomely. It always gives them someone to play with. I have 3 yorkies, 2 chis' , and a pug. I'd even love more! I have enough love for them all
But seriously, it always takes a bit for a new addition and the older furkid to adjust, but in no time, in my house, they are happy and playing like they knew eachother forever!