First up is the excellent utility vim-markdown-toc. As I use Vim and Markdown intensively for my own personal and professional documentation, this utility is extremely useful.
You can generate a table of contents at the top of a Markdown document with a simple command like GenTocGFM and can easily remove it with RemoveToc.
To follow table of contents links in Vim you shift + k.
Second is vim-markdown which does folding and syntax highlighting for fenced code. It is so useful for documenting code that I cannot think of not having it.
To install both just clone the Git repos into ~/.vim/pack/plugins/start/