If i were you, i would take the truck after you purchase it to a Dodge dealership at least 1 time & let them suggest what needs to be done.
After that do what you want to do as to services. If you decide to do your own servicing, then you will know what Dodge suggested & decide on your own what to do
You may be fortunate & the previous owner always had the service done by the dealership & you would have an up to date service record
2009 Ram 1500 SLT QC, HEMI , 3.55 axle, Bushwacker flares, soft tonneau, Line_X, DEBO Step, Mag-Hytec, Weathertech mats
2016 Ram 3.0 diesel 3.55 w/LSD, G2 tonneau, Line-X, Weathertech mats, Mag-Hytec differential cover, Nfab bars, CB radio, Autonet wi-fi router, EGR bug deflector