I would like some users to NOT have access to the blog in a certain space. Is that possible?
Yes, it’s possible and very easy to do. If you know already how to restrict a page, it’s the same process.
On a published blog you go to: the three dots on the top Confluence menu and click Restrictions. There you can choose who you want to restrict.
More about blogs in the Atlassian documentation: https://confluence.atlassian.com/doc/blog-posts-834222533.html