Wow that's a lot of questions.
I will answer the ones I know but I am new to RVing but not to towing.
-When you hitch tailgate down after you hitch tailgate up!
-The "Stupid" looking tailgates are so you don't have to drop and lift the tailgate and you cant damage the tailgate by forgetting and it keeps anything from falling out.
-I don't know if there is a way to lock it into the truck but I will likely be using a cable to hold mine from disappearing along with the geny.
-The scissor jacks should be just for stability they have a landing gear to hold up the front end.
-The brochure should have the specs on height.
-YES I would worry about all bridges and tunnels that are lower than standard height.
-Yes you still require a trailer brake controller
-The CAT scales seem to be the choice for weighing your rig.
-As for the propane I would think it would be the same as your travel trailers.
Hope these answer some of your questions but here's a suggestion if you search out some key words in the search section you will find lots of past treads on many of your questions.