Whenever i try to download a mod for my rust server hosted by AGS, it tries to open in the visual studios app. I am not sure how to fix it this isue. 

Sounds like you have Visual Studio set as a default for .cs files. https://www.digitaltrends.com/computing/how-to-change-file-associations/

Ark Gaming Servers resells GTX servers at a 25% markup.

Source: When I had AGS I saw GTX's branding on a page and found the same server for 25% less and switched to them.