Additives aren't necessary at all. The Ram has good filtration. In the winter you might want to add some anti-gel if you get super cold temps, but nothing else is needed. Ram specifically states that additional additives are not recommended.
Fuel filters are actually a mileage based change, not a time. Every 15K miles they need to be changed. There is a Ram dealer from down south that sells OEM fuel filters for about $100 (as of last year). Its easy enough to change yourself. I buy the filters and invest about 30-45 minutes of time and save $400.
Oil and filters... my truck is essentially used for towing only so I put about 8k miles a year on it. I change my oil once a year, not every 6 months. Some will yell at me, I'm okay with it. I tow 10K lbs and I'm not pushing my truck with weight, speed or heat. I'll probably get an oil analysis done right before my next change just to confirm that everything is still doing fine. The filter is accessible from the right front wheel well, behind the plastic shield. It can be a little annoying to get to, especially because the recommend pre-filling the filter before installing.
Exhaust brake. I use it every single trip. Actually, I turn on tow/haul and exhaust brake every trip. T/H saves the truck from lugging the engine in town. EB saves on the service brakes. T/H and EB makes the braking more aggressive. If you plan ahead a little, you can use the EB to slow you from highway speeds to 20 mph, then service brakes the rest of the way. Towing in the hills/mountains... EB is AMAZING! An occasional gentle tap (literally a 1 second tap) of the service brakes will downshift the truck and engage more aggressive EB feature when going downhill. I love it. I don't need the diesel for my current trailer and don't ever expect to tow massive heavy trailers... but that EB and ease of doing downhill will likely keep me in a diesel for life.
