That's an awesome setup! CPU/RAM upgrade capable is a plus

and I love the 2.5 inch bays in the rear for an SSD boot drive. :D
I chose the 16bay 836 over the 12bay model only because of a great deal offered from a local vendor, for me, it is pure overkill.
With the capacity of hard drives today, I will never require more storage than 16bays will provide.
In your case, I would choose the 16bay rather than adding a JBOD for future expansion of the 12bay. IMHO adding all that hardware (back plane,
cables, power supplies, etc.) introduces too many points of failure and is much more costly when compared to the price difference between 826 vs. 836.
I assume it's probably a bit noisier than the SC836 but it's going to be in a work room in the garage in it's own rack so it's probably not a big issue unless it starts vibrating the house :)
lol
As far as the noise difference between the two models, I've not had the opportunity to personally compare them. Maybe someone else would care to
comment on that subject.