I'm getting 15 MPG on Deisel and Propane is running about 3.49/gal. Insurance is about $600/yr.
Except in certain circumstances, you can run 4 down with a toad as long as it has a manual transmission. If you use a dolly it increases your towed weight. My max tow weight is 3500 lb and the Class 2 (2") tow receptacle can take 350# on it. You will most certainly need a towing brake system which runs north of $1000.
So far I have bought one starting battery, one house battery and a couple of miscellaneous body parts.