Moving from 3 to 4 kids in a blended family

My partner has two girls (4 and 6) and I have a boy (5) so together we have 3. We have the girls every second weekend and half of every holidays, and our son lives with us and sees his dad every second weekend and half holidays. The kids are With their other parent on the same weekend cycle so we have all 3 kids together. We are wanting to have another baby together to complete our family but unsure about going from 3 to 4 kids. How much adjustment is needed, Expenses, housing, transport, time management, one on one time with kids etc.