With my old TT I got around 8 mpg. It was 31' and weighted 7,000 lbs max but usually less. Same truck and the 5er listed in signature I still get around 8 mpg but I tow about 5 mph less. The 5er has a gross weight of 13,500 lbs, near the top limits for one ton gas engines. Usually aluminum is lighter than fiberglass. I bought mine as a E-bay auction repo, picked it up highway 400 north of Atlanta.
Some 5er's have a computer desk area. I would attend any RV show and look, look, look. Take notes of ones you like. There are floor plans in both that will fit your needs. If the high ceilings are a must, then it's a 5th wheel in your future.
Our old TT had one slide with just a couch in that area. The 5er has 3 and we love the extra room. After spending 2 months in it this last winter we couldn't go back to a TT. The 5er is so much easier to hitch, pull and back. 5er's generally have more storage. Our's has lots of cabinets and then there's the basments. Basements in a 5er are the area under the bedroom and just behind the hitch, some are huge but most offer a large storage area.
If you want counter space, so 5ers have L shaped, U shaped and even islands in the kitchen area, some island are mounted on rollers and are movable. You'll find one you love. If you'll both be cooking together the U shaped might be to tight.
Welcome to more confusion.