Can I remove the install.sh file that has been hanging out at the root of my system since install?
Of course. Once Virtualmin is installed, install.sh is dead to you–it should never, ever, be run on a system that is already installed. So there is no good that can come of having it lying around. You might be tempted to run it again, for old times sake. 
Thanks Joe!
…it’s…tempting…me… 
No the system is working great so I will banish that file!