This seems fun at first, but then a bunch of concerns come up. Notion is not a real database. You're dependent on Notion uptime _and_ WonderSites services; 2 very weak links in the chain. There are no docs whatsoever; does the site build every time a change happens in Notion, or do you push to production?
Looks cool for a quick POC of a web agency but beyond that, things seem highly unreliable.