I had a 2000 3.0L Ranger 5 speed. Good truck. Dipwad not paying attention to stopped traffic in front of him decided I needed a different truck in '06.... Great little pickup until the end though.
I can tell you 100% certainty, do NOT get a Ford with the 5.4L 3V engine. What a horrible design that was. I love my '04 F150, I HATE the engine...
Your respiratory issues can be a huge problem buying used as tobacco smoke residue tends to reside in the soft components for years, if not decades.
Knowing the truck you are towing with, yeah, the size trailer you are going for makes a LOT of sense...
IF the budget allows and you come by one though, a bus might not be that unreasonable. There is a 4 row short bus Chevy cab, I think Wayne or Thomas for sale close to me for less than $2K in pretty good shape... Too small for my needs, but I see these come up pretty often on the cheap...