Hi,
You can use the content templates feature to place content anywhere in your blog posts. A separate field isn't really required for this.
The Blog feature has supported "Related Posts" since 2.3.9.3 I believe. You can find a setting for this in the module settings and the related posts will show up on the post view page. Related posts are all those which are in a category the post is also in.
HTH,
Joe D.