"Turing completeness is necessary for intelligent life." Sure, but it would be extremely difficult to write a simulator with "interesting feedback" that is not turing complete ...

"In our universe, the speed of light is the speed of causality" In your simulation the step function is causality. I would not be too concerned if the simulator was not strict in conservation. As a matter of fact, the interesting parts of our universe have the property that they are in the middle of an entropy flow.

Just some random advice, maybe you don't find it useful, but I would not focus too much on these things ...