Ok, reporting on my findings
First of all, it's already 10 times better. My mouse is now, close to normal even though I feel some lag/hiccup/freeze now and then, but not close to anything I was experiencing earlier yesterday
What I did: I went back to the drawing board and downloaded the latest EFI from the first post of this thread.
Then I compared the config.plist from
The everything works Asus Z390-I Gaming * i7-8700K * SAPPHIRE NITRO+ Radeon RX Vega 64 Build
That's when I realized that the USBMap.kext xml entry was actually NOT enabled ! *headslap*
That's why I wasn't getting my custom port mapping registered !
Anyways, after verifying my custom port mapping (that I previously had assembled), I also disabled the 2 port limit patches in config.plist
--> I now have a working USB (and Bluetooth) Catalina install inside my shiny new case
I am going to run like this for a little bit and if the mouse lagging problems persist, I will look into maybe tinkering the framebuffer stuff.
Thank you everybody for your help and hopefully my posts can help somebody else