We have an article on ways to do this here.
We have an article on how to do this here.
The Audience Insights tool can be a great resource to analyze different potential audience groups in more detail. Meta has general information on this tool here.
Lookalike audiences update automatically every 3 to 7 days, as long as you’re still actively targeting ads to the audience.
Website custom audiences update automatically as people who fall within the specified rules navigate to your page. Other custom audiences may require manual updates of the underlying source audience or may utilize third party update tools for more automated updates (such as Zapier).