Correct in that both nurseries and universities are a simple on/off switch of sorts. You need at least 1 nursery for children to be born. You need at least 1 university for children to turn into workers.
You also need universities to train classes of workers into scientists, so yes, more universities can mean more classes. I tend to build 2 universities for later in the game when you have excess population and can benefit from faster research.
You do get a small benefit from additional nurseries in that they lower the death rate for kids. It acts like a low capacity medical center just for kids. You're better off building medical centers. Medical center have a greater impact at reducing mortality, and they do so for your entire population, not just kids. Additionally, a medical center takes just as many workers/scientists to run.
The biggest impact on population growth seems to be morale. High morale also lowers death rate, which indirectly increases the birth rate since the birth rate is also dependent on population size. High morale and medical centers can greatly speed up population growth. The one downside to medical centers is they take people to run, which are in short supply early in the game.
If you don't research things like recreational facilities and forums, they don't impact your morale. They do however reduce the impact of other negative colony conditions, such as housing shortages, however, if you're properly managing your colony, this shouldn't be an issue. I put off researching morale specific buildings until the every end of the game.
Event morale can easily overpower colony conditions morale. Hence spamming goods from a consumer goods factory can get you pretty darn good morale, even if everything else is falling apart. On the downside, going to war and killing enemy "good" buildings, such as residences, is the fastest way to tank your morale. Do this and you can expect to have awful morale for a very long time. There is exponential falloff over time for event related morale, but it can still stack quite a bit and take some time to fall off.
Smaller events, such as new kids, new Command Center being completed, or killing enemy "bad" buildings can also improve event morale a little bit, though the effects are not so large. Similarly bad events such as people dying, your buildings being destroyed, or disasters occurring can lower event morale. Researching disaster warning systems will lessen the impact of disasters to event morale.
You may notice there is a bit of a feedback loop between population and morale. Good morale produces more kids and fewer deaths. Meanwhile new kids adds to morale, while deaths would subtract from morale.
Finally, workers contribute twice as much towards new kids as scientists do. So don't be too eager to train a lot of scientists early game.
