Well, yeah, it would be nice if ECC had become a standard RAM throughout the PC industry.
But the way it is now, you would need to spend a significant extra just for the "luxury" of having it in your system.
It's NOT necessary to have it in a home NAS.
It will not make much of a difference for your overall data resiliency.
What you should be concerned is with the ability to recover from the far more likely to happen events such as:
user errors (accidental deletion), lightning strikes, electrical surges, fires, floods, earthquakes etc, etc...
Why would you need to limit power?
To save your CPU from overheating?
Low TDP doesn't mean higher efficiency.
TDP - thermal design profile.
Your Node 804 has more than enough room for a chunky CPU cooler - no reason to limit anything.
Your CPU will fall back into its idle state as soon as it's done doing the work.
A low TDP CPU will not save electricity - might actually consume more since it will keep the rest of the system stay active for longer.