Hardware RAID has died years ago.
Nope, still widely used. Though, the tendency these days is to use RAID1 (Simple mirroring) or RAID10 (Mirror+stripe)
RAID5 has largely bit the dust because it was found to be less of a data protection than was thought. Plus, failure of the RAID controller itself leaves you with a perfectly intact but mysterious collection 1's and 0's that no other computer can make sense of
I got two RAID-6 arrays though with 8x 2TB and 6x 3TB WD Reds respectively, each on one Broadcom MegaRAID 9271-8iCC. RAID-6 have two parities instead of one, tolerating up to two drive failures without losing data.
High RAID levels will likely need hardware RAID controllers due to the computing overhead, especially when older hardware is involved (like my home server based on a Core 2 Quad Q9300). You can still use RAID-5 or RAID-6 with big drives, but you need to be careful to stagger their potential failure dates. I bought my drives at different times, giving me a nice staggered production date spread and thus a potentially staggered failure dates. I also have a reliable hardware supplier that can ship me a WD Red within a day. And I have a cold spare of a 2TB and a 3TB drive ready. This way I can replace the failed drive ASAP if it happened, and RMA the failed one for a replacement.
To keep your hardware RAID card last longer you need beefy cooling. RAID cards run very hot and need a proper server case with good airflow to cool. Since I need to keep my machines quiet, I usually just strap a fan right on the card to tame the heat, using some localized airflow through a quieter fan.
As of the ECC memory, you may want to check if the motherboard supports it or not before buying it or using it as a server that requires it. Some consumer-oriented motherboards with server-class chipsets (like this X58 one, or some newer ones with C232/C236) does not route the additional pins needed for ECC memory, making the board fundamentally incompatible with them. Also check the maximum allowed memory capacity before buying anything.
If you intended to use this machine as a server, you may want to use a low end, low power graphics card in it, or go with the integrated graphics if it has one. GTX 570 is a power hungry beast.