We have three because we wanted three. One's in secondary, one's in primary, and one's in nursery.
Yes, our children get enough time, attention, and resources from us. We don't struggle with time; we both have well-paid jobs and are progressed enough in our careers to have had more flexible schedules even prior to the pandemic. I don't find it difficult to give each child individual attention. They all have different personalities and get individual attention at different times, from both DH and from me. Same with money, we knew that our expenses would increase and we were prepared.
We needed a larger car, and there are nursery fees for now, but we had room for those things so it wasn't really a consideration, more of a fact and an adjustment on my budget spreadsheet. As it turned out, the pandemic made things easier -- shorter commutes (or no commute) meant fewer hours at nursery and no more need for wraparound care so it's much cheaper. I'm not spending those hours on a train now, I'm spending them with the DC. DH does the school runs and nursery dropoff now. I'm home before 5 pm. It's terrific.
We didn't need a bigger house. We rearranged the layout a bit so everyone got their own bedroom (and DH and I get our own bath!) and while we certainly looked at larger properties, neither of us are keen to buy while everything is overpriced.
Now that DC3 is here, the family feels "complete". There's a rightness about it that's difficult to describe. That's not to say there aren't chaotic moments, but they pass, and things settle.