The bigger the waste tanks the more weight when they are full. Watch your payload and RAWR on this one. Remember, everything you add will increase weight.
The major things for us are usable, comfortable toilet, large shower, lots of counter space in the kitchen and a comfortable walk around bed that is easy to make in the morning.
We had an outdoor kitchen and didn't use it as much as we thought we would.
No need for solar or a second battery if you do not plan on boondocking for days. We have overnighted in parking lots a few times and our single 110AH battery served us well.
If we still had a TT a power jack would be a must have.
Our power awning is horrible in the wind, very flimsy. Our manual awning in a previous TT was sturdy and adjustable. The one we have now is a piece of poo.
I like the warm lighting our interior LED lights provide over the incandescent bulbs it came with. We do not boondock but the LED lighting is a nice upgrade.
Enjoy you adventure