Gee, bobby - you think regular gas will make his diesel start better? Hmm. Let me think about that for a second - no.
affordable001- cavitation is an issue on diesel engines - you can do some research but basically the coolants have additives that help prevent it. The green requires frequent checking with test strips, additives, and frequent changes. Ford Gold requires less checking and less frequent additives, but has some issues with gelling and clogging oil coolers, especially on the 6.0 engines. There are several International approved extended life coolants (Such as Cat ELC, Rotella ELC, Delo ELC and others - read that post I linked above) that can run for hundreds of thousands of miles between changes and don't have the issues that the green and gold do. I run Shell Rotella ELC in my truck.
Your buddy is referencing the 5W40 synthetic motor oil - it will help it start easier in ultra cold climates (remember - that's relative to where I'm at - ultra cold to me is below 50°...) Unless you regularly see freezing conditions - don't worry about it. Some guys run 15W40 during summer and 5W40 during winter. I run 15W40 year round. For the two or three days it plunges below 50°, I could plug it in if I thought about it..