I don't think there is a set number of animals that you should own. I believe these are two important factors to consider:
1.
Can you afford to take care of them? This is not limited to the initial purchase price -- I'm talking about maintenance. Monthly heartworm pill, flea and tick preventative, annual shots, grooming, etc. not to mention wee wee pads (if you use them), food and treats. Clothes are a luxury but they cost a lot too. Also, what about emergency situations?? What if your dog needed rush emergency surgery tomorrow and it would cost $2,000? If you have too many animals, you may not be able to afford this for each one.
2.
Do you have enough time and energy to give them all equal attention?
If you can afford financially to own 6 dogs but don't have time for them, then 6 is too much. If you have time for 6 dogs but can't financially afford that many, then 6 is still too much. You have to find a balance with your finances and time and be fair to your dog.
I thought about all this (and MUCH more) before I decided to get a third dog. I had to put the dog FIRST before my own selfish longing for another baby. I'm telling you, it's that PUPPY BREATH!! You can't get enough of it!!
