To addressr the Jegs tech statement that there is no such thing as
oil to cold. I would challenge that statement because
oil by design flows best at higher temps and
oil needs to be hot enough to help disapate any moisture in your system. I have had two well know engine builders that have told me that your oil should be anywhere from 140-240 degrees in order for it to work properly. 12AN is a good size because in some cases a 10 AN might restrict your oil flow and increase your oil temp. Wait until your weather warms up to decide to change fittings. I can't answer your other questions but I bet someone else will.
Clois