Hello Dan and welcome to the forum.
You are gonna love your new unit if you buy it.
Let me answer your questions.
Yes the TV will swivel 360 degrees so you can watch from dinette, bunks, or couch. You can add a larger TV but the way it is set up now you can stow it for travel. I take mine off as I want more cushion on the TV and am not a fan of it possibly bouncing around. A larger one would also need to be slid off this swivel bracket. The Tele uses a typical V shaped mount bracket that other RV TV's use.
Ceiling lights are all individual.
The TV will play thru its own speaker. DVD's played on the TV will play thru the camper speakers.
I have not moved mine but I doubt you would be able to move too many HW pop ups. These suckers tend to be heavy.
The screens will keep out bugs but yes, pop ups will have certain areas where a bug could crawl in. I doubt you would ever stop that.
I have not noticed any problems with the door width. As you mentioned they do tend to be standard. Older Coleman's with the wall steps do have a couple inches more.
I use a WDH just because when I first bought my popup I had never towed before and people said having anti sway would ease my concerns. The WD finction was required/ recommended by my auto manufacturer.
I hope this helps.
I too bought my camper sight unseen. I am in Boston and I could not find one within 1,000 miles. These things just sell too quick to ever find one.
2006 HW256 (previous pup)
2013 Chevy Tahoe
Equalizer WDH 1000#