I like using the badges available in your MyPage on the old Sims3 site as a guide. It'll set you on some journeys of discovery. Some of my videos are based around the badges available. And as a bonus, you get extra goodies to add to your game for the first few badges you manage to complete successfully. But you have to be logged into the site to get the badges awarded.
Apart from that, I'd buy an Alister's Alchemy Station and start your sims looking for ingredients. They can study alchemy by clicking on the station, and can start making elixirs with it if they have the knowledge and ingredients. There are two of them in this picture - there is a witch in the background working on the station, and a human sim in the middle of the picture holding up an elixir she's just made.
https://i.postimg.cc/XJQGvH9t/Dianna015.jpg
Another thing, unless you've got the various occult types turned off in Options, and by default they are turned on, your townie sims will be turned into occults by the game. I always have them turned off as I like to control who becomes an occult. But Moonlight Falls comes with a few occult households so you will have them there anyway. I have a lot of fun with my Supernaturals and hope you will too.
EDIT: In my signature there are pictures of some of my various video series. The McFluff story is all about a witch and her 15 cats.
The Isla Paradiso Bunch has genies as well as a witch and mermaids. Genies come with Supernatural. Mermaids with Island Paradise. The picture I posted above is from 'The Isla Paradiso Bunch' videos.
