The level of raid is fundamental to the operation of your raid array.

As I recall, RAID 0 is striping. It will give you faster throughput because your array can pull values out of multiple drives at once. RAID 1 is mirroring. In that, half of the drives are used for data, and the other half are used to back up the first half. RAID 5 is parody, and that's what you're looking for. Essentially, your drives will mostly be used for storing data come up with the last one will be used to track what information is on the other four, so you will have one drive for redundancy and the other four will be storing data.

Hardware raid versus software raid matters to the extent that parity calculations are relatively expensive and so if you're trying to do RAID 5 on software raid, that's going to eat up more of your CPU power and reduce your drive throughput.

I don't recall truenas in particular, and what you using the nas for is really what is important, but I do recall that some Nas software doesn't even want you to be using hardware raid because it will be using its own software algorithms that are separate from what you would typically consider to be raid.