Not sure why you need such a fancy raid system. I have lots of different footage from HD ,1080p. some at 130 Mbps from a hacked GH2 to 4K footage from a GH4. I am using a regular thunderbolt drive 3tb with my i5 mini with the HD4000 card. Works fine.
Biggest limitation on these machines is the graphic card but if you max out the ram you'll bump up the card's memory to 1Gb. My other Mini, an i7 model had a built in AMD card with 256Mb or ram and it could not reliably play back 4k without stuttering. Even so you gotta realize that even editing a 1100 clip project using native playback, a lot of compound clips and no transcoding can be done on a mini, the secret I believe it the maxed out RAM and the internal fast SSD.
No if you're going to get crazy and have a number of multi cam 4k clips then yes you're going to perhaps need a raid and then I doubt the graphics card could handle it even with the raid and clips transcoded.
Your GPU will be your bottleneck. 16GB RAM min. SSDs are small, so a RAID would be a waste. A single T'bolt drive, SSD or SATA would be fine. An SATA based RAID would be fine. But that GPU will be the wall you eventually hit. But editing with proxy media will go a long way to helping.
A fast 'deliever' would be the #1 on my shopping list.
depending on wallet-size, this could be an amateurish, <100€ usb3-software-raid as mine, or a >5k$ Pegasus...
Concerning 'speed' ... is that of any issue? You're no news-room, I assume. You're not doing high-coomplex 90min features with tons of effects&compos? And even if so: Does it really matter to 'wait' (=you could do other things meanwhile...) 40min instead of 20min? If it matters, you should get paid for 'speed' and consider investement into a speed-beast MacPro.-