For your mirrored drives idea: I've had two nvme drives in mirror for a while but there are a lot of caveats to getting maximum performance. Not sure how it is on the AMD side but most Intel boards for example would have one m2 slot connected to the CPU and the other three via the chipset. Which makes them share a common bottleneck (also with your 10gb ethernet card)

For me it was in the end much faster to get a new board with pcie 5.0 support and a large enough single SSD. Total IOPS and throughput both turned out higher than my previous RAID 0 array.