There is no simple answer. The OP mentioned a two-drive G-Tech, that's probably the G-RAID, available in various capacities but commonly 8TB. It is pretty good, uses software RAID -- either built-in AppleRAID or you can use SoftRAID:
https://www.softraid.com/
In general I'd recommend Thunderbolt over USB 3 because it seems a bit more reliable, plus they are easy to configure due to daisy-chaining. However USB 3 drives or even arrays are OK in some cases. I have about 20 of the Seagate Backup Plus Fast 4TB drives and they are very handy and relatively fast for a bus-powered drive:
https://www.amazon.com/dp/B00HXAV0X6/ref=cm_sw_r_cp_ep_dp_Lekjzb2DJ6RT3
However for serious work you normally want an AC-powered drive using external power, not a bus-powered drive.
For RAID-5 a good choice is the OWC Thunderbay 4 series. They are available in various capacities from 4TB to 40TB:
https://eshop.macsales.com/shop/Thunderbolt/External-Drive/OWC/ThunderBay-4. You use SoftRAID with those, which works very well and avoids tying you to a proprietary RAID format. With hardware RAID if the chassis fails you can't put those drives in any other brand of enclosure; with SoftRAID you can. SoftRAID is as fast as hardware RAID, or faster in some cases.
For highest performance SSD RAID-0 is good. One of the least expensive ways to achieve that is the OWC Thunderbay 4 Mini chassis plus adding your own SSD drives such as the Samsung 850 EVO. It's under $3000 for 8TB if you build it that way.
https://eshop.macsales.com/shop/Thunderbolt/External-Drive/OWC/ThunderBay-4-mini
https://www.amazon.com/dp/B010QD6W9I/ref=cm_sw_r_cp_ep_dp_Q8jjzbEDYEDZF
If cost was no object, I'd have all SSD storage. 40TB is available from OWC pre-configured for $28,000:
https://eshop.macsales.com/shop/Thunderbolt/External-Drive/OWC/ThunderBay-4-mini-RAID5
If I needed shared or NAS storage for FCPX video editing, the best products are from LumaForge:
https://lumaforge.com/jellyfish/
Direct attached storage is usually faster and less expensive than NAS but NAS has some benefits. My 8TB SSD RAID-0 array does about 1500 MB/sec write, 1860 MB/sec read, which would be difficult to achieve using a NAS. However LumaForge NAS products are specifically optimized for FCPX and can achieve extremely high performance due special I/O and caching methods.
Spinning RAID arrays can be very fast for sequential transfers, and that covers a lot of video editing. However there is a significant subset of video editing that involves small random I/Os such as when FCPX is making database calls. That's where SSD really is beneficial.
You're right it's important to (1) Plan ahead and (2) Always back up, even if using redundant RAID.