I am late to the party, as usual, and you've had good advice so far so I will add just a couple of simple things.
IMHO. If you look for a tag axle, Aqua-Hot and Air leveling you will also find the other quality things you are looking for. I am also partial to the Roadmaster Chassis and the Dyno Max chassis. Put those together with the floor plan you like and enjoy. The house items are similar across the manufactures and the drive train, if maintained, will run nearly forever. As you mention, used is much better than not used.
I think the 2004-6 Dynasty's are a sweet spot for value, of course it is all very personal choice.
Best Wishes!