Can a zero hour pilot actually launch a Bombardier Q400 with only simulator experience?
You don't even need your own simulator. Here is a good video of how to start a Q400 (taken from a sim game) and here is one from a tech going through an actual cockpit. There is even a chance there were checklists in the aircraft when he arrived. 

To get off the ground he really just needed to know how to gun the throttles and roughly when to pull back on the yoke to get airborne. These numbers can be found pretty readily around the web. Considering his fuel and cargo load and depending on the trim of the aircraft it may have even started flying with almost no control inputs.  

Whats important to understand about some of the maneuvers he did was the fact that the aircraft was empty and flying on a partial fuel load which will make it easier to do some of those things. I will refrain from diving deep here until the NTSB report is out but at full throttle planes are capable of quite a bit. Rolling an airliner is not out of the question in the right scenario.