Gridsome is a static site generator by heart, but since its using Vue.js for frontend means you can add any dynamic content on top of the static content. This makes it possible to build any kind of CDN-ready websites and serverless apps with it.
Gridsome can generate thousands of pages in seconds so you can build pretty large sites without any problems. You need to think of the build process is almost the same as waiting for the cache to propagate. It's strongly recommended to use a CI tool like Netlify or AWS Amplify Console to auto re-build site on content changes.
This is not easy right now without building custom solutions. There will be simple preview services in the future that will make this easy.