How many is too many?

My husband and myself have 3 girls aged 5, 4, 2.

After a lot of discussion we have both think we want another, not trying for a boy, just want another bub for our family but how many is too many?

Am I selfish wanting another baby, is it just hormones talking? Will I have enough attention to give another baby or will one of my other kids lose out?

Confused here and would appreciate some perspective.

Thanks!