Going from a static site generator (Jekyll or Hugo) to Craft CMS; Export/migrations options?
There is a good plugin called FeedMe that can help with imports. We used it migrating a pretty large EE site without issue. If you can spit out a XML, RSS, ATOM or JSON feed, it should be able to import it.

FeedMe Plugin

I am not sure if it is Craft 3 ready yet, though.