Just set you hostname as a fqdn. For example mail.example.com or webserver.example.com. You also may want to enable swap on your droplet. Digital ocean frowns on it as it wears out their SSD's, but I would and do setup a 1 gig swap. They don't encourage it, it is allowed and worth it as a backup just incase it is needed.
I also setup fail2ban on server and use https://wordpress.org/plugins/wp-fail2ban/
There is another tutorial that rtcamp put out that I folow...Here it is. https://easyengine.io/tutorials/linux/sysctl-conf/
Look through all of those tutorials, Rahul's tutorials have taught me so much over the years.
I also use ufw to manage iptables but thats about it for webserver. Also setting up ssl with easyengine is dead simple so now that your site is up you can use letsencrypt and set tls up on your site.
Best of luck