You shouldn't ever need to add anything to your fuel tank except fuel, save for the one off possibility you get stuck in an extreme cold snap with fuel that's not blended for the climate. In 30 years of construction and 1000s of diesel powered engines, I've seen this happen exactly once. So not a general concern at all.
Fuel filters are mileage based 10-15k miles generally are the maint intervals. Again not obtrusive or difficult, although some of the newer trucks have more expensive filters. You may spend $100 buying a set of filters or waaay more if you're a take it to the dealer kind of person.
Guess I don't think diesels are generally all that finicky, but I've been around them long enough that theyre common place to me.