That’s a really good question. The AMD related topics appear to be spread across those two forums.
Unfortunately, the last time I built an AMD system, it was shortly after the wheel had been invented.

I’m also much more of a budget computing kind of guy - I guess that’s because I’m a Scot at heart. So I’m not going to be much use when it comes to all those premium components. RGB is also not really my thing, either. But not to worry. I’m confident that there are lots of experienced users in the two forums you mentioned.
I guess my biggest advice for you is to not jump into that ”new tech” pond until you start to see a clear trend of maturing BIOS releases. In my opinion, there are simply too many low-level incompatibles at present. And I’m sure that you don’t want to add any more stress to your life if you can avoid it. Hopefully, the shop you get to build your new system will be both competent and a great resource for the life of the system.
In regards to you AIO choice, make sure it is compatible with the latest MSI motherboards. The Arctic LF3 is an odd animal compared to the previous gen. Check the Arctic website for more details.