This mod itself does not fix this, simler90's mod does.

Townies, meaning homeless sims, yes. The game will still create them as needed, such as when creating role sims or coworkers. They serve no other purpose in the game, so there's no compelling reason for EA SP to create more than necessary.

There is the "Increase Vampire Population" action in the MoonlightFalls file, you can find it using Ctrl+F.

Thank u!!

I saw that SP can create new families to move into the city. How does that work? Can they create large families or just small ones? I saw that in my current game, a new family moved in, but it's only one Sim. If it's possible to increase and adjust these proportions, how do I do that?

Furthermore, I would like to adjust how often Sims move house, but I would have to change the categories to adjust the delay. Regarding this, is it just a matter of changing the action category? Or is there a deeper adjustment?

It definitely shouldn't only create small families. Typically, single-sim move-ins are caused by the role manager, not by SP. You can stop this by creating a tuning mod that modifies the "NpcRoles" XML. In this file, change all occurrences of the word "Residents" to "Townies". Alternatively, you can simply install NRaas Register, which disables this behavior by default.

You don't need to change the category of the "Create and Move In" action, simply adjust the delays located just above it, under the "Create Household" action (these values will automatically apply to "Create and Move In" as well). The value you want to change is Delay_Min. The Delay_Max value should be equal or greater than Delay_Min. Just to clarify: the delay doesn't determine how often the action occurs. It just tells SP that if the specified number of days hasn't passed since the last time the action ran, then the action shouldn't run again. Whether SP chooses to consider this action at all depends on the current demographics.