Late 2012 iMac + GeForce eGPU (Windows/MacOS)?  

I have a late 2012 iMac with the following MacOS setup (as well as Bootcamp Windows 18xx):

And I had some questions:

• Under Windows, I believe I have no issues running a Geforce eGPU?
• Under Windows can I run the eGPU through the main monitor?
• Can a GeForce card work at all under MacOS Catalina - even if its an older GeForce model (I believe no)?
• Under macOS, if I used an AMD eGPU, can I run it through the built-in monitor?

Thanks all.