First, welcome to the RV adventure.
Since you stated you are first time RV owners, I will mention some basics.
If you are not sure when the unit was serviced last do it now. Needless to say check your manual for recommended service intervals.
This includes engine, transmission, hydraulic system (cooling fan if equipped) oil and filters. We have an Allison 3000 transmission and service interval is just 24k for conventional and 50k for synthetic since it has a engine brake. So if it hasn’t been done it’s probably way overdue.
Check coolant, test SCAs since it is a diesel. Or you can flush and covert OAT based if you want to avoid SCA maintenance.
If your air dryer filter is more than 3 years old I would change it as well, but again check your manual.
I change my fuel filter annually and carry a spare in case I get bad fuel somewhere.
Open up charger/inverter and make sure all electrical connections are tight. These will work loose from all the vibration while traveling. A loose connection will burn up the connector. I will also inspect the connections in the battery compartment. I check mine every couple years.
Fill and test your batteries.
Check and reseal roof, vents, skylight, marker lights, and windows as needed. Water is one of your biggest enemies.
Service generator if needed.
Check age of tires so you know when they will be up for replacement.
That will get you started. Good luck.
2002 American Eagle 40M
ISL400 / Spartan MM
2003 Jeep Liberty/2019 Jeep Trailhawk