"Should I install fail2ban on my droplet?" Yes.

Have you tried Googling this? A quick query found Tutorial: Securing Webmin. Webmin/Virtualmin has a big following; I'm sure there are plenty of other articles available via Google.

You'd prob. be better served by first doing a Google search, yourself; and THEN posting on here when you come across something you'd like help with. You'd then be in a position to cite to the info. you'd like help with, so that others on here can take a look at it first, so that they can offer educated assistance.

thanks for your reply @pablo, I don't go anywhere until I ask my dear google about my doubts,I think the mistake I did was I was searching for virtualmin instead of webmin. even though there is no how to steps to change the port no :10000 to something else.
As I am a nooob in linux it is very difficult for me to understand where about's of the linux commands etc.
What is found is the link http://www.virtualmin.com/documentation/security/faq where the similar thing is given as your link.

Take a look at this article: http://blog.serverbuddies.com/changing-the-webmin-port/