In the Sims 4, they never supported mods.

And I've had some bad times with downloading a lot of skins.

#1:
You download too many, and you may not even be able choose a face.

I've downloaded too many skins, and they covered up the faces on the faces option, So, my advice that would be:
MAKE 2 VERSIONS!!

2 bc if somebody downloads too many faces it could cause the skin-tone picker to grow and get so long that it covers up the faces.

So, a second version is the way to go when creating mods that are skin-tones, or have skin-tones.

#2: Don't download too many and download the skin detail versions

I used to want to only download ones that weren't skin details until I learned better, now I hope to find some that are simply skin details.

The cause of this is bc the game is programmed in a way that instead of creating a scroller for extra skins, it just increases the amount of skins, without the scroller. You can choose them, but it grows larger the more skins with you download and if you download too many they might cover up all of your faces.

Let's say you might want an Asian face, if you download too many it'll cover up the faces options the way that you won't be able to pick the face that you want.

I don't know how it goes with eyes...but...you may want to be careful with those, too...

Well, you could use the mod that increases the CAS columns. I ran across this with eyes, but I fixed with 4 columns. xD Of course, I don't have a real massive amount of eyes, like, enough to cover up the eyes completely. With 4 columns, it just gets to around half the space.

This is a warning better suited for a place that’s...not a modding site.

The official forums are full of vanilla users that have never modded before. I think this information would be more helpful for some of them