I think our Titanium is around 12K and we have had no problems. I did some quick research before we bought ours and it seems like over 35 ft is when you start having some problems finding a site. With our 34 ft fiver we haven't had any problems in private CG but you will see some in State and National parks.
As for ease of moving, I don't seem why it would make much difference. The process is exactly the same for a 40 footer and a 32 footer. Maneuvering around tight areas would be more difficult with the extra length. Inside towns and parking lots mainly. And of course driving around CG roads which can be tight.
I have no feel for fuel consumption vs weight. One major factor is the large frontal area causing a lot of drag. But that would be the same no matter how long the trailer is.
