Welcome to the forum!
1) Can't help you with the price
2) Looks like the kitchen & sofa are on the slide. 30" is OK
3) The AC load can depend on if your site is shaded or not.
4) What hitch and brake controller are they installing? For a trailer that size I'd want an Equalizer or Reese Dual Cam and a Prodigy brake control.
5) The spec says it has a 30A service, forget the 50A cord but you may want a 30A extension cord.
I'm a bit worried you'll be under-trucked for the trailer though. 2 adults, 3 kids, a bed full of gear, and a 34' trailer towed by a 1/2 ton sounds marginal. What's the payload rating on the truck? Now subtract passengers, gear, tongue weight, and hitch weight and you'll probably be in negative territory.
Let me guess - the dealer said "Sure, you can tow that, no problem." It's up to YOU to determine what your trucks capacity is.
