Nvidia → AMD and 10.12 → Upgrade. Order/Cautions?

Hi folks.

I've been running a very stable vanilla Nvidia-based Hack for a couple years now on 10.12 (first Hackintosh), but I haven't attempted an OS upgrade or any hardware changes yet.

Specs:

• i7 6700K (Skylake) CPU
• Gigabyte Z170 UDH TB board
• GTX 1080 GPU
• macOS on SATA SSD; Windows on m.2
• Older version of Clover... Not sure which; have never upgraded
• iMac 17,1 SMBIOS

I'd like to get this thing up to 10.14, so I've purchased a Radeon Vega 64 (MSI AirBoost reference design model, as recommended by the Mojave GPU Buyer's Guide post awhile back).

I always keep a bootable clone of the drive in the system (using Carbon Copy Cloner) and update it before I make any system-level change, like security patches.

I'm planning on taking this opportunity to update/clean up my Clover setup, following the newest version of the Vanilla Guide.

So here's the question:

What's the best way/order to do this upgrade?

• Would it make sense to change the GPU to the AMD card first, make sure everything is running, then attempt a standard OS upgrade? Can the Vega64 even be used on 10.12?
• Would it make more sense to get the Clover stuff updated while retaining Nvidia support, then attempt OS upgrade, and use the basic system drivers (are there any???) to see what I'm doing after the OS upgrade, and then do the GPU swap?
• Is this all just too dangerous-sounding, and I should really just go back down to bare metal and start from scratch? And if so, would it make sense to still just do the Clover update/cleanup before that, or after? What are the implications for Windows booting? I can easily live without a Mac (I have a bunch more if I really need macOS), but I can't survive without a booting main computer. *Are there any implications for iCloud? I finally have iMessage, etc. working, by not being an idiot and using someone else's SN (the first time, I didn't realize that you *want the Apple coverage check to return "invalid!"—I kept generating them until I got "valid!" I feel terrible if some poor sap couldn't use iCloud on his legitimately-purchased iMac...).

Some of these questions might be embarrassingly naïve, and for that I apologize, but I think I'm at the Hackintosh level where I know enough to get the overall ideas, but expect that as soon as I wade into the process, I'll hit questions I didn't know to ask... Just trying to straighten the road here and map out the best route from here to there!