1. I'm 6'3" about 195 and have no problem, but I always have my seat reclined to the back, if you sit straight up you may have less headroom than you like but test drive should make it clear for you. Headrest is pushed way too far for my liking, but that could be fixed and you'll know after driving if it's good for you anyway, just remember the seat is 6 ways, can go up and down as well.
2. I have no kids yet, but I don't see why not?
3. If you like the leather, get the leather, you live only once.
4. I average about 38 for the lifetime but it can vary greatly even in the same conditions. For example this morning going to work 30 miles, traffic was ok most of the time but dense, I averaged 45 mpg, the same way going back home, traffic was really bad especially in some spots, I barely got 37mpg. One thing for sure: a lot of short trips, very fast, hard highway driving, you won't break any mpg records. My personal theory: if you met old EPA ratings on your previous cars, you should meet EPA ratings in TCH, if you didn't, then you should get similar percentage wise drop. You'll get lower mpg in winter by few miles.