Without entering the truck/weight police discussion....
Space in a TC is at a premium. Dogs? May be able to live with 3 ankle biters in a small TC, but I wouldn't even consider it with one large dog.
Room for more than 2 people semi comfortably leads me towards a longer/slide out model which either isn't do able with a short box truck or very heavy for the truck you have.
Fuel mileage, with my truck I get about the same with the TC on the back as I do pulling a high profile trailer. I'd expect less than 10mpg with any hard side camper on a gasser.
Space and amenities are all in the eye of the beholder. Only you can decide if it's enough room for you guys and the dogs + kids once in a while. Wet bath that you can literally sh t, shower and shave at the the same time without moving could be a drawback.
We, family of 4, came from tent camping, so a TC seems luxurious, but pets don't come with and we don't use it much. It is comfortable for extended trips, we've done up to 3 weeks in it and it's super fun and the TC configuration fits our style. Back country camping a lot, a trailer would be a limitation, but we have the option of towing toys. Don't do that often or far though as the truck is pretty maxed out.