I've owned a Thor Chateau 22E for 3 months and 1800 miles. I'm happy so far. It's only 24 ft bumper to bumper but includes everything we need for comfortable travel.
An E-450 chassis would only increase the GVWR. Generally not necessary on shorter lengths.
The MPG is horrible so if fuel economy is an issue, refrain from purchasing any RV.
I keep reading about Ford E-Series Cutaway Handling issues but can't say I've noticed anything unusual.
Leveling systems are not necessary on shorter lengths.
The length of a unit does impact handling.
Traction control is available but you would almost certainly need to special order to get it.
http://www.ford.com/commercial-trucks/eseries-cutaway/features/ 