A) a servo wheel turns about 90 degrees;
OK
B) the more overall rotation of the servo arm the greater the resolution of the control;
Yep, if you dial down the "volume", it really just reduces the number of digital steps. Still, there are a LOT of digital steps. THe resolution change is more academic than apparent.

C) more up than down is preferred for the aileron;
Yep, on a flat-bottom wing especially.
D) little or no down aileron with mostly up is preferred in a model, to help prevent stall out and diving in opposite direction to control input.
No, it's to reduce adverse yaw, where the down-moving aileron acts as an airbrake and the fuselage yaws, for example, left, when the pilot is commanding a bank to the right.

For differential travel: If you are using a single central aileron servo, and you set your pushrod connections at the 3:00 and 9:00 position on the servo wheel, you should get equal travel up and down. If you set the pushrod connections at 10:30 and 1:30, you will get almost all up and almost no down.