And if a person wants to understand why something is done one way and not another, they need to figure it out themselves.
There's nothing complicated about it: take a piece of paper, a pencil, and play, recording all the construction costs (you can use Art-Money or codes to add resources and gold and build the city). This way, you'll learn what and how much you need (similarly, you can determine at what point you'll need a rare resource). It's unlikely that you'll be able to conquer mercury, sulfur, etc., on Veteran difficulty in the first week playing as "Haven," so you need to determine how much of them you need to gather by a certain day of construction.
I can't say anything more specific right now – it's been a while since I played as them.