I don't consider myself an expert on RAID - I've used 0/1/5 in various situations and I'm planning on adding one to my build soon so I've been doing a good amount of reading.
I see a lot of warnings against RAID 5 due to the increased chance of rebuild errors as storage capacities increase (should a drive fail). I'm not here to judge, but if you haven't done a good amount of homework comparing RAID 5 to RAID 10, I'd recommend it. Personally after all the reading I've done on the subject in the last few weeks, when I saw you planning to do 20TB RAID 5, I panicked a little envisioning the anxiety of losing that much data due to a rebuild error.
Other than that, it looks like an absolutely fantastic build.
Best of luck!