I think the size of the house/property in general would be more important that the number of bedrooms. We currently live in a 3 bedroom house, but it's on a half block so the house is quite small. We're already worrying about it being too small once the baby is born, but it's because of the overall size, not the number of bedrooms itms?

Me and my sisters all took turns sharing rooms growing up and didn't get our own rooms until my parents renovated and added a 4th bedroom when we were 12, 9 and 7.