If I install Virtualmin as a stand alone install and then later install Webmin will there be an issue that Virtualmin is not installed as a Webmin module?
Will I lose any functionality?
Will i be able to see the link to Virtualmin in Webmin?
Virtualmin is a module that runs on top of Webmin.
So, if you have Virtualmin running, Webmin is there too 
-Eric