96 E350 15 passenger with 351W I get 14 mpg with 15 people inside. It alright but not for pull heavy trailer since rear axle have 3.55. It would tow if I have 4.10 in axle.
any E350 with 5.4L could get 14-20 mpg on how you drive but for tow it would be 8-15 mpg. If V10 you be struggle to get 12 mpg.
E150 I wouldn't dare to pull no more than 6,000 pounds they are too light.
E250 cargo you could get under $3,000.