How can I hide search results until the user submits the exposed form?
You can change that under Advanced Views options (third column): Exposed form style:



After you choose Input required, you can adjust further options, including the text to display before any filters are active: 





If you're using Better Exposed Filters module it has an option for it too: 


  Input required
  Only display results after the user has selected a
  filter option.




It hasn't changed since D7, it works the same in D8 as it did in D7.