Well, I can address DEF: it's a fluid that's added to a seperate tank and helps diesels burn cleaner. As someone who basically hates diesels - it makes them not stink
😉How much you use depends on how the vehicle is used - but a 5-to-10-gallon tankful of DEF generally lasts a long time. Months, in many cases. And when you need more, it's readily found at any truck stop, Walmart, etc. You can find a DEF pump that looks like a fuel pump at diesel islands; or you can buy it by the 2-gallon jug and add it with a funnel.
Most vehicles will give you a HUGE warning before you run out - something to the effect of "300 miles to empty"
Ed, Deb, and 2 dogs
Looking for a small Class C!