I understand it will be different for everyone! But what would you say? We aren’t in a position to consider an age gap any shorter than almost 4 years. DC1 will be one of the oldest in their school year, if that makes a difference, so the waiting for bigger one in school idea would mean 5 year gap - plus is it maybe less than ideal for them to deal with starting school and a new baby in the house at the same time?
I love the idea they might enjoy some shared experiences together and play together sometimes, though this isn’t guaranteed I know. I also like the idea of one on one time with each.