I have found a few Intel mATX motherboards with 6x SATA slots at 220-250 euros, but all of them have Realtek networking. AMD AM4/AM5 had Intel networking. What exactly is the reason why you have chosen the Intel CPU? Why is Realtek something to avoid? What is more important here? The CPU or the Networking? Also also, I would like to avoid Gen12 and Gen13 Intel CPUs, because of the recent issue with them dying. That was the reason why I chose AMD in my original choice.
Do I need more than 32GB for NAS?
Found LSI 9300 8i with 4x for 99 USD on Amazon, and the Intel motherboard with 6x SATA was 220-250 (but Realtek network), so price-wise your choice is cheaper. I think I may go with it.
What do you mean by "flashing it"? Do I need to change the original BIOS on the extension card? Doesn't it work as plug and play?
If so, can you please explain that to me? What BIOS, from where and with what tools? I have never flashed the BIOS besides the motherboard.
Cheers