I have about 450 sims in my game, and I never even knew I had to do anything about it? I used the "sims limit" before, but got rid of it when I realized I could not restrict my population growth. So instead it all went out of control. Now I have a played household on most residential lot, and I have most of the worlds.
I normally marry sims who already exists.
I play on rotation and I spend more time with households that I like.
I use extra DNA, and some sims turn out infertile, meaning less reproduction. Most couples gets just 1-2 kids, but then there is the nobility that needs multiple descendants in order to secure their wealth and power.