Very interesting build! I would love to try this.
Just to put the ca calibration at rest you could just use a battery with a light bulb in series to limit current and an amp meter in series to compare with what the ca sais.
In regards to using the cro for a mid drive. Have you thought about using a mxus 3kw or maybe the leaf 1500w. The leaf will allow 6000w in burst and has reached 60mph at 72v in the wheel! These two options would be much lighter than the cro and if you only want to go 50-60mph the cro might be overkill.
I am very interested to see the difference between the DD hubs and the geared in a mid drive set up.
There is no doubt that the geared is better for climbing, but I bet the DD would be better for a city speedster.
I wonder if lugging would be tolerated better by the DD as appose to the geared since it doesn't have the gear bearings.
Also if you could fix the rear free wheel as well, that would allow for regen.
Though I don't know if regen would work with the derailleur.

(dose anybody know if this works?)
Worst case if you want regen it could be just one fixed gear.
Someone really needs to develop a derailleur that can be used with regen.
This one new invention would be a game changer.
O what about internal geared hubs with a fixed freewheel! It's like getting two birds!
You'd have the best chain line all the time and gears!

Shifting through the gears is just fun 8)
What do you guy's think?