Oh boy. This is kind of a land mine when it comes to getting recommendations.
The first thing that you have to address is EXACTLY what your goal is. If you are primarily building a gaming first workstation second computer that will have significant differences from if you are building a home NAS server where you one garunteed data accuracy/security.
In my personal experience the majority of crashes, stutters, and freezes I have experienced since I started building computers in the 90's have been software related and nothing to do with hardware. I've still got a Pentium 4 running Windows XP SP2 that is bullet proof and never gives me any problems. It also doubles
as a great space heater. I would do your best to create a good system. UT understand that there may still be all the things you have experiences because it's software not hardware.
As a general rule of thumb last generation hardware is going to be where you want to look. It is new enough that the performance will be good enough for the vast majority of things you want to accomplish and because of its age (in theory) has had enough time for bugs to have been ironed out and firmware/software fixes created.
Regarding CSM motherboards. They are not more stable than any other type of motherboard. It is a program designed to ensure companies can have a long lifespan on the same hardware because the manufacture gives a garuntee that they will continue manufacturing the part. The manufacturer also makes the promise that they will give a 6 month end of life warning for any SKU that they will be discontinuing so that enterprises have the opportunity to plan for upgrades to their systems if required.
ECC is great if your data is super important to you and you can't have any loss whatsoever, even a single bit or two. I personally have never run ECC on my home rigs and the only issue I have ever had that I traced to my RAM was my computer crashing when doing large video renders. Turned out one of my sticks was functionally dead. Put any kind of load on it and it would just shut down and be unresponsive. No amount of ECC would fix that kind of issue.
There is evidence that ECC RAM can lead to overall high latency and power frame times during gaming but unless you are playing at 240hz at e-sports competition levels you probably won't notice. Depending on what motherboard you choose make sure to check if it supports registered or unregistered Ram of you go the route of ECC. This will impact both your options available to you and the cost of the Ram.
If you can find ECC that's compatible with your motherboard of choice and isn't that much more expensive then go for it. Can't really hurt anything.
Powersupply: The highest rated Seasonic power supply you can afford and a UPC. Check for the 80+ rating, in order from best to least (least here means still REALLY good but not as amazing) : Titanium - Platinum - Gold - Bronze. Try to get one larger than you system needs NOT because it means it's more stable or efficient but rather so that if you upgrade down the line you don't have to touch the power supply.
Dual redundant is only necessary if you are looking for as close to 100% uptime as possible and you literally cannot shut down your computer because you will lose money or data. Dual PSU will allow you to swap out a dead one for a fresh one with no downtime. That's why they exist, no other reason.
Raid M.2 is a perfectly good idea but a good rule of thumb is to have your operating system on the boot drive and ABSOLUTELY nothing else. Have SSD's for your programs and games. When running multiple SSD's and M.2s and GPU's (depending on your situation) you might need to keep an eye out on how many PCI lanes you are filling up.
I air cool probably the way to go for you. I'm a Noctua shill and I'm proud of it. I love their black editions of their fans and the NH-D15 is kind of the king of covering all your bases for colling needs. The silence is a major selling point as well.