Is it better to upgrade the career rooms as soon as you can or wait? Does it really help their salary grow faster?

It certainly helps the peeps get promotion faster. It's particularly noticeable at the beginning of a career, which I why I'll usually only upgrade a room when a new generation takes over. I'll wait to upgrade until I'm sure that the family can afford it, and only upgrade a room that will be used. Because of that I've had, say, a L1 workshop and a L3 office in the past.

Thank you. I'm really enjoying this game. I have 5 families now. One generation 6. I've had 3 sets of twins and one triplets so far! I'm going to try to do a "mod" on my house today.