iMac 2015 27" 5k - Best Setup for Internal Display  

So I'm mainly referring to this topic, which didn't give much info. ( https://egpu.io/forums/which-gear-should-i-buy/imac-2015-27-5k-best-setup-for-internal-display/which-gear-should-i-buy/imac-late-2015-5k-27-with-rx-5700-xt/)

Apparently, as of Windows 10 1803, you don't need to use a headless adapter to accelerate the internal display of an iMac with an eGPU to play games, as I love my iMac and I would rather not use an external monitor! I'd be okay with a performance hit as long as the overall performance is better than the original R9 M390.

This topic appears to accomplish this pretty well! ( https://egpu.io/forums/builds/2012-imac-21-5-3-5ghz-i7-16gb-ram-1tb-hd-akitio-node-gtx-1080ti/)

My iMac doesn't have an iGPU (like that last post with the 2012 iMac), just the dedicated R9 M390. 

So.. my question is, are there any cards and enclosures that work the best with this method? I have a GTX 1080 lying around to test it (before I buy a newer GPU for this) and was thinking of getting a Sonnet Breakway, but I'm not sure what model to use. The builds section here reports the 350 and 550 both work, but I'd like to know the best enclosure even if it's not sonnet! Given the I/O of the 2015 iMac, I'd buy an Apple TB3>2 and a TB2 cable to connect it.

So there's the hardware side, regarding software, is Windows 10 1803 the best to install for Bootcamp? As the message on the top of this site is claiming Device Mananger error 12's after updating to 1903, so should I stick with 1803/1809? Once that's installed, what would the process be to get it to work with the internal display? Would I need to delete the M390 via device manager and restart? Or would it simply be plug and play, and use the Windows Graphics Switcher introduced in 1803 to accelerate my games on the internal display?

Thanks so much guys! I'm sure answers here would massively help out others who have similar setups.