Don't overstress yourself on the save game stuff. I've broken every rule in the book and never had a problem <knock on wood> in a year and a half of playing.
I've saved with a convoy only a few km away, near land, under attack from destroyers, submerged, surfaced, damaged, and in the middle of the Atlantic thousands of km from land and ships.
I'm sure it will happen to me eventually but I don't lay awake at night worrying about it.
Welcome aboard!