Just the normal stuff in a used RV. Make sure all of the appliances work, as well as the slide-out, genny, A/C, etc.
There are no serious issues for this rig that I have found.
I live about an hour from the Thor plant, and last fall took a tour of the factory. I was able to sit down for 2 hours with one of the senior builders (not the design staff but the construction staff). Learned a lot of information as to how everything is assembled.
One thing though - if you are not used to driving a motorhome, they are all pretty finicky. You will typically not drive it faster than 60mph as being a high profile vehicle, there is a lot of wind-buffeting and wander in the steering. Part of this is the geometery of the vehicle, part because of the weight loading, and part due to other factors.
On a windy day, especially with a cross-wind, you might be "white-knuckled" after driving on the interstate.
Typically a front-end alignment and upgraded sway bars will help a lot in making the vehicle drive better. I am sure it will feel a lot different than your 5th wheel, and if you have not yet test drove it at highway speeds, do so before signing on the dotted line.
Two of my future projects is to put upgraded sway bars on the vehicle as well as hydraulic lifts. As the vehicle sits, there are no jacks to level it, so you have to be discriminating which RV campsite you get. Currently I carry along some home-made ramps made of 2x10s, but after one season - that has gotten very old, and we will be having Bigfoot levelers installed over the winter.
I like to keep the rig level as the slide-out works better and is less prone to jamb, the fridge needs to be more-or-less level, and my Egg's Benedict just don't come out right if they are lopsided.
The other issue we are fighting right now is more ergonomic than anything else. As you are driving down the road, all of the pots, pans, and anything else not tied down makes a huge racket as they bounce around. This of course is not noticeable in a 5th wheel as you don't hear it, but due to the nature of a motorhome - that racket can drive you nuts.
So you will learn where and how to store stuff to make the minimum amount of noise.
The only thing that works on a RV is the owner...