Census models require nothing other than a data source connection. Once you've got any data source connected (except Google Sheets, which sadly doesn't run SQL yet!), you can immediately start creating Census models.
You can think of Census models as a fast way to write and reference a SQL query. You can write a brand new query or copy-and-paste one from an existing system. Give it a name and save it, and you can immediately start using your model as a source for any of your syncs.
We like to think of Census models as a shortcut. It's meant to get you started with modeling quickly. But if you have a more complex set of models in mind, take a look at our dbt or Looker model sources.