I personally would like 4. I grew up in a trio but my little sister was so left out because my big sister and I were always together. But on the other and I am in no rush to have a third. I am nearing 40 and if it happens it happens, if not....that's the way things are.
I don't believe financially that having a second put us in huge financial difficulties. Things are tight but it will only be temporary. DD2 is wearing DD1's clothes and uses DD1's highchair, stroller, bouncer, toys etc... We have reusuable nappies. The only thing that impacts us is daycare and that will only be for a year or less as DD1 will be going to school soon.
For holidays, we tend to rent an appartment or a gite so in terms of costs it doesn't change anything for us to have two kids instead of one.