As someone who has a fair number of close friends, I think this is a good post with lots of solid advice. And it's written well! Personally I've been lucky to just naturally meet and form my best friends over time, but I definitely think taking initiative and following up are important to maintaining a close friendship.
A general point in this post I also like is that making and keeping close friends may require work and energy, rather than being something that life just throws your way. I intentionally try to periodically message friends, come out to places they live, just generally keep in touch; as one gets older people move about and it's harder to maintain your closest friendships, but it is possible!
Last comment: this is a very pragmatic and analytical post with a lot of discussions of things you can do, and not much discussion of how you should feel. I'd add this - just CARE. Appreciate the people in your life and let that appreciation guide you.