One of my favorite topics.
Start here. It's a great tome on Raid, why Raid is not a backup, but for fault tolerance, and details about the different Raids, their pros and cons, stipe size, etc. Lloyd Chambers is a wizard and a Mac guy.
I currently use
SoftRaid for a couple reasons: 1) Lloyd recommends it as one of the best, and 2)It comes "free" when you buy an excellent OWC
ThunderBay4. I'm glad you found them. In my opinion, you can keep looking at other options, but you'll end up back at Softraid.
I use Softraid on a four bay, 3.5" 16 terabyte (4TB x 4) Thunderbolt 2 external ThunderBay4 in a Raid 5 configuration. I'm still using El Capitian on my production/office computer because of excessive
Apple Core Rot.
I only have two volumes on it: Data and TM (TimeMachine). Fewer volumes makes
automatic CCC backups easier
. All my data: pictures, website code, tax documents, everything, is on the Data volume. That not only makes backups easier, but then, only having the OS on the internal SSD makes operating system upgrades fast, easy, and doesn't hold my data hostage if there is a crisis during upgrade.
When I ordered my ThunderBay4, I ordered it with four 4TB drives, and then ordered a 5th identical drive as a cold spare. It sits in the office desk drawer. If there is ever a drive failure, I can pop it out, pop the new one in, and the Raid will rebuild. I can do this without much worry because even if the data gets corrupted during the rebuild, my latest backup would have run the night before.
If you have the bucks, SSD sounds really awesome (pun intended). Not only is it faster and more energy efficient than spinning platters, it's
quieter. I will say though, that I don't notice any lag with using 7200 RPM 3.5" disks. Opening a 100,000+ photo catalog in Lightroom doesn't have any issue. I only buy reputable ones from places like OWC (currently Hitachi). I
do not buy the enterprise class drives, because with Raid, I think that money is wasted.
Networking: because I leave my iMac on 24/7 thanks to WeatherCat, the Data volume is "on the network" and easily found by other computers if they are needed. With open ports, I SFTP into it from Hong Kong without problems. The point being, that NAS with an ethernet port isn't really necessary today, and Cat5/6 is sloooooooow compared to Thunderbolt 2. Thunderbolt 3 is on the way to things like Macs and storage devices, but who knows when it will really arrive. If you aren't in a hurry, you might try reading the tea leaves on it and decide if you think it's worth it to wait. Remember, it will be pricey.
I'm no expert, but have been happy with the setup I have. It's quite reliable, fast, and has worked really well. Let me know if you have other questions that I can try to answer. I'm also looking forward to other's setups so I can learn more, too!