@Carnival-Boy Hi Carnival.. is it something that is easy to do? It may seem daunting at first but it is pretty easy. I would start here.. with this tutorial..
https://developers.google.com/maps/documentation/javascript/store-locator
The trick is building the MYSQL table getting it to spit out XML from a .PHP which is all outlined how to do that. Then it is just a matter of importing the .csv or creating a page that can interact with your MySQL database to update it. This is actually how I have created several of these types of maps for different companies and my own.. I actually don't even know what you mean by importing the map and a Google Sheet.. I have not done it that way before. Are you referring to Fusion tables? Sort of lost on how you set yours up originally. Sounds time consuming and difficult.