PM schedule, maintenance logging, and warning signs for a city-driving box truck

[Stella_R]

I recently started a small delivery business with a used medium-duty box truck, and I'm trying to establish a rigorous preventative maintenance schedule to avoid costly breakdowns and keep it on the road reliably. Beyond the basics like oil and filters, I'm unsure what specific components on a commercial diesel vehicle, like the turbocharger, EGR system, or air brakes, need regular attention that a typical car owner wouldn't consider. For owner-operators or fleet mechanics, what are the critical inspection points and service intervals for a work truck that sees mostly stop-and-go city driving? How do you log and track maintenance effectively, and are there any particular warning signs or sounds I should be listening for that indicate a minor issue is about to become a major repair?