Has anyone had experience building a Drupal 8 site?
I have. DM me if you want to discuss further.
Plenty on AngelList ;)
The first thing is to hang out where developers hang out. Try reading forums like StackOverflow and get to know some of the personalities that talk about issues important to you.
While you can find competent Drupal developers all over the world, you haven't provided any information about what you want them to do with Drupal. Some types of sites are much easier to build and run than others. And some functions require different focused skills.