Went from an 18 foot, to a 31 foot, to a 35 1/2 foot trailer. My total length now is 58 1/2 feet. Add the cargo carrier on the back of the trailer, and it's another 2 feet.
I have found the longest trailer to be the easiest to tow. Because of the long wheel base of my truck, backing into camping spots is really easier than with the shorter 31 foot trailer, and MUCH easier than the 18 foot trailer.
About campsites? If you have a longer trailer, yes ... you do have to plan a little more careful where you camp at. But we have always been able to get a campsite anywhere we set our hearts on. We do have to be selective on our actual camp site, and sometimes we pick spots that are not so wooded so we have better space for maneuverability to park. But we've always been able to get a spot. Now that we no longer have Dish Satellite TV, we'll probably be parking under trees a lot more now. We gave up our DishTV and went back to over-the-air. We're looking forward to getting more in the tree lines again.
By the way, those 31 to 35 foot trailers look big ... only in the show room. Once you get them outside, they REALLY aren't all the big any more. And when you pull up beside a Semi Truck with a 53 foot box car in tow, you feel like a dwarf beside them.
What I'm saying is, don't be afraid of getting the 32 foot trailer for the shorter one. But if the shorter one really fits your needs, then by all means get it.
About your kids. Look for a TT that has the full size bunk beds. They are usually corner bunk beds, but they do provide more space for the kids to stretch out on. Rear bunkhouse style campers, generally still have narrow bunks, designed for kids under 10 years old.
Oh, one more thing.... You may hold a CDL and may have driven multiple tractors and trailers. But when you are towing your OWN camper with your own vehicle, it's a totally different ball game. There is always a sense of heightened paranoia - anticipation, especially when your family is riding with you. (and this is a good thing). But, it definitely not like driving a commercial truck. It just a different animal when it's yours.