I’m working on something similar at the moment. I’ve decided on using radio buttons or a dropdown to ensure a user has to pick from my taxonomy terms when creating their post.
I’m still refinig my solution, but these two articles have helped me a lot:
http://themefoundation.com/wordpress-meta-boxes-guide/
I want my metabox to appear in multiple post types so I’ve used this too:
https://wordpress.org/ideas/topic/add-meta-box-to-multiple-post-types
Hope this helps. I will endeavour to update if I change the example code in the articles significantly.