Yes, it's another "what hardware do I need" post. Thank you in advance for your patience.

I multiboxed 5 shaman in TBC on a Dell laptop. I think it's about time I tried again.

I'm looking to upgrade my PC with the goal of multiboxing eight mages in Classic WoW. Here's my current configuration:

Code:
CPU:              AMD Ryzen 5 2600
Cooler:           Corsair H115i PRO
Motherboard:      Asus ROG Crosshair VII Hero
Memory:           G.Skill Trident Z DDR4-3600 (2x8GB)
Boot Drive:       Samsung 970 Evo 500GB M.2-2280 NVME SSD
Game Drive:       Samsung 860 QVO 2TB 2.5" SSD
Junk Drive:       Seagate Barracuda Green 2TB 3.5" 5900RPM HD
Graphics Card:    See below
Case:             NZXT S340 Midi-ATX Tower
PSU:              Seasonic FOCUS Plus Gold 850W 80+ Gold
Operating System: Windows 10 Home 1909
Monitor:          Acer XB270HU 27" 2560x1440 144Hz
I currently have access to two graphics cards, neither of which I'm particularly happy with from a stability or power point of view. These are: MSI RX 570 ARMOR OC 8GB & Sapphire Radeon RX VEGA 64 8 GB NITRO+

It's generally a solid PC with a few teething troubles. The first is the graphics card(s) which, with a little TLC, might turn out to be viable options but, frankly, I've had my fill of AMD and want to return to NVIDIA. The second is the case which, I suspect, isn't doing an optimal job of getting the heat out (or, more specifically, getting the cool in).

Aside from those issues, I feel, that to support eight accounts with reasonable graphics settings (Setting 3 - Classic Mode - with 60fps on the main and 30fps on the slaves) I'll need to upgrade my processor and RAM.

The question is, what is required and where am I most lacking?

As far as RAM is concerned, I feel another 16GB would be a good upgrade, but should I add another two sticks of the RAM I have or replace what I have with a 2x16GB setup?

For the processor, I'm thinking of a 3900X might be the way to go. I do like the 3700X, particularly because it has a lower TDP, but I'm not sure it's a worthwhile upgrade over the 2600.

For the graphics card, I'm looking at a 2080 Super or a 2080Ti.

My questions are:

1. Are my proposed upgrades sound? Will they do the job?
2. Are they, perhaps, overkill? Can I get away with spending less?
3. Where will I get the most bang for my buck? Which upgrades should I prioritize of the others?
4. 4x8GB or 2x16GB?

My goals are to have a 100% stable platform from a hardware point of view. I can't be doing with resolving stability issues; that's just not fun for me.

Thanks in advance for your help.