My uses for my future truck are similar to yours so I'll add a few thoughts...take it with a grain of salt as my truck is currently on order but I previously had a 2500 followed by a 3500 DRW with air ride and now I have a 3500 SRW w/ air ride on order. The reason I did the 3500 DRW is I also have an Arctic Fox truck camper...but my family has out grown it so it's getting displaced.
1) I'm glad your doing your research on the hitch weights for the ORVs...as you stated...ORV is know to have very high hitch wights once fully configured. The model I'm looking at is the 21DBS and owners are reporting hitch weights of 1200#~1300# before they even get to max trailer weight...I remember reading someone stating they had 1/2 a tank of fresh water and scaled it at 1200#...which most don't expect for a 21' class trailer. I've read of a few people had to get new tow rigs because they didn't expect such a high hitch weight. I would expect something similar for the trailer you are looking to get...prob keep that in mind when you are purchasing your wt. dist. hitch as well.
2) The payload ratings are a bit conservative on the modern RAM 2500s but only you can decide if you are comfortable exceeding those numbers. As you mentioned, many people do, some out of ignorance some out of calculated risk to get that "better" ride quality. Ride quality is very subjective, I personally didn't mind the day to day ride of the 1 ton and would (and have) daily drive my truck but my other vehicles tend to have suspensions that are valved more aggressively and have a bit of "platform" to them (you mentioned MTB so I'm hoping you understand the reference) so they tend to ride "harsh" or firm to most people. Even with the air ride, unless you decide to go the carli route in the future, plush will never be a descriptor used for the ride quality.
3) Similar to DRAGRAM, toyed with using the alt ride height but eventually didn't bother with it
4) I agree, an often overlooked huge plus of the CTD is the exhaust brake...the drama free decents are worth the price of admission.
5) Be mindful that your 15 mile commute is actually a bad thing when it comes to a CTD. I wouldn't use it as a reason to go gasser, probably much to do about nothing for most people...if anything it will give you an excuse to do your weekend ride.
6) I personally have toyed with the idea but loading a motorcycle into the bed of a truck using ramps gives me enough anxiety so it has been nothing more than an idea. I have seen pictures of people but no one I know has tried, putting on a diamongback cover and loading their bikes ontop of that...seems very iffy to me but something to think about if you need the bed storage for large coolers and such.
7) One last thing, if you are one to modify your vehicles, the rear air makes suspension modifications a bit of a challenge. Not saying it cannot be done but you have to be more thoughtful because it's not as common and aftermarket support isn't as wide spread. (i.e. aftermarket shock options are limited, etc).
Long story short...you are going down a similar path as me...my answer was a 3500 Mega Cab CTD SRW.