Regarding #3, I wouldn't worry to much about information from the '70s about diesel trucks. That was ALMOST 50 years ago.
I owned my '05 Duramax for 3 years before I found out it had a block heater. It always started and I didn't have a garage then. Yes, it cranks a little slower when it's below zero outside but it's never failed to start.
I grew up on a farm with tractors and eqipment, spent some time as an OTR truck driver, and have been driving diesel Chevy's for 13 years. I have never put anything but diesel fuel into a tank except for my generator. That fuel has been in there for 4 years now so I did put some conditioner in it. For engines that are used at least once a year I wouldn't worry about it.