You are in luck - I recently build myself new desktop and had similar doubts/questions so did a lot of research. Take make advice as very subjective as I’m not an expert in every detail. Most cases though we have similar requirements, so I hope you will get something out of below.
CPU:
As for CPU - unless Intel will make some kind of huge comeback there is nothing better you can buy on the market then 5950x. Right now AMD has all the bases covered - both no of cores/threads and single core performance (for gamedev more cores is better then single core performance / for gaming - still single core performance is most important on CPU). I also got 5950x. It’s expensive, but for me it’s worth it especially for Unreal work. “Compiling shaders” message is not as annoying as it used to be. I think you could go with 5900x as well, which is significantly cheaper (but less cores).
GPU.
3090 is overkill for most applications*. If you can get your hands on 3080 then get this one. Or wait a bit as there are rumors of 3080 ti which should be almost as performant as 3090, but with 20gb of VRAM.
In theory 2x 3080 is more powerful in comparison to 3090 aside from memory (6k cuda cores more, 4gb of VRAM less). Though it’s not that simple as other factors come in, like data exchange between cards, no. of PCIe lanes that you have available etc. And the biggest problem is how to fit 2 3080 in the case and motherboard - those are big cards, so keep that in mind. I think for rendering on GPU (CUDA/Optix) you should get better performance out of 2x 3080 vs 1x 3090. For “general” game-dev one of the GPUs would sit idle.
The “*” I put close to overkill is because I got one 
. One of the few application that 3090 is not an overkill is deep learning and I dabble in that too.
(side note SLI is dead -> and only available on 3090 now IIRC)
“Question 2 - RTX 3080 – Is it enough with 64-128gb of ram?”
For comfortable game-dev 32GB of RAM is more then enough. I don’t know what you would like to do to utilize 64 or more, unless you have some specific use case for that. And yes, single 3080 should be enough even if you get 256GB of RAM.
And for this question: “Just want to know if a 5950x and ONE 3080 is enough to have comfortable lesson experiences and future game dev”
Definitely it’s more then enough. I think that 5800x and 1 x 3070 would give you very comfortable experience. 5950x + 3080 is almost the best possible experience right now (better only would be 3090, or 2x 3080 but aside from rendering time in cycles - you will not see huge difference).
And some random comments:
- get very fast SSD (m2). Or a couple of them. That will improve your unreal/unity experience more than new CPU or GPU. Currently I think the best one is Samsung 980 Evo pro. Samsung is solid brand in terms of SSDs. If you need loads of storage also buy big hdd. Make sure you are buying pci gen 4.
- There are huge supply issues with new GPUs and CPUs. In most part of the world getting your hands one one is nearly impossible.
- Watch couple of independent reviews (like from Jaz2c or GamerNexus).
- Buy very good PSU with room to spare on the voltage. 3080/3090 are power hungry beasts. Plus with cheap PSU you risk stability issues. Surprisingly there are also supply issues in many parts of the world for PSUs.
- Don’t cheap out on motherboard, but don’t overspent here either unless you plan to do some crazy overclocking. Check if it has all the features you need (e.g., if it have enough PCIe 4.0 lanes to support at the same time all SSDs and GPUs if you will decide to go with 2x GPU or if there is enough physical space to fit 2 GPUs). I think the strix board is good, but even the TUF ones should be good if it meets your other requirements.
- RAM - recently sweet spot of performance vs price is around 3600Mhz / CL16/17. But maybe it changed atm. Check timings and number of channels and number of ranks. Also check compatibility. I don’t think it’s issue anymore, but AMD used to have problems with it in last gen. Don’t forget to turn on XPM profile in your bios to get full speed out of it.
- Invest in good cooling solution. Either go noctuna or similar (or water cooling) on CPU. 3080/3090 + 5950x is a hot combo.
. I would finish it with “… last computer for next 3 years” 
). This is my first water cooled system and I was really hesitant to go this route. I’m quite satisfied with the choice due to efficiency and noise levels (though when the 3090’s fans start to spin up then it really makes no difference 
it is a loud card).
