@Sharonia : It´s not difficult to install a custom world. Nearly all of them are installed via the Launcher (there is a small % of worlds which don´t come as Sims 3 packs, they are world files, these are installed differently, but I would concentrate on the other 99% of worlds)
If you download a world which you like, you just need to double click on the world data
(the file looks like the ones in the picture, the ones with the green plumbob in front of them)
https://i.imgur.com/aupRAik.jpg
and the Launcher opens itself and installs the world. That´s all you have to do if you like to install a world. (sorry for the German, but I hope it helps :) )
But: you don´t have so many EPs, so you have to be careful, which world you would like to install, you have to read which EPs you have to own to be able to play the world. Sometimes you´ll just miss some deco objects, but if a creator uses a bridge from an EP you don´t have, you can´t access all parts of the world and the Sims will get stuck. Then the world will be unplayable.