If you're only looking at 5-10k miles a year, just plan on an oil change and all filters (oil, fuel, air, coolant, and air dryer). If you want to keep this simple and cost-effective, just find a Speedco and you'll be out the door for all of it under $500 plus air filter and air dryer. If you want to spend more, find a Cummins or RV dealer that thinks you have blank checks to pass out. Cummins builds a solid motor, but each model has had some issues that have been mostly weeded out through TSB's and recalls. I'd at least have the serial number checked for any recalls or major work performed that's not being revealed. I'd go for having an oil sample tested.
https://www.speedco.com/en-us/the-speedco-experience/rv-services
In my book the older diesels are much better. The DPF's, EGR's and common rail systems today do not create a 500k mile motor anymore.