Yeah, you have missed a lot, not surprizing, given the ocean of info here.
First off, the Ebike CA simulator has the Cute 328 as a motor choice, so you can plug in your parameters and get the answers you seek.
But, of course, given an opportunity, I will kibitz.
You don't tell us if you are building a bike or a trike, so I searched your posts and it looks like a trike, but that is not listed on the sim anyway.
Concerning the Voltage, depends on how fast you want to go;
A 36 V pack will get about 20 mph.
A 52 V pack will top out a little over 26 mph.
There is an efficiency curve as well, but I can tell you things like, how fast you go, your weight and aero and rolling resistance will have a much greater effect than swapping controllers.
As far as taking the Q100 apart, I've been inside all the 36 V variants and have several posts showing the innards. Here's one by me that is more info than pics and a really old one by lynchy (cell-man) that goes back to when the Q100's first came out;
If you are interested in pedaling (PAS)< you might want to look at the 17 A and 20 A "KT" sine wave controllers from PWS Power. They are a great match for the Q100.