Hello JulStaR13.
For the sim you have very precious information regarding procedures on career.aero, in your "download" section. There is the Sim pitch/power table and also a brief description of the mission.
For your questions :
You don't have to play with the mixture. It stays full rich at all time.
I had no experience on PA34, did my MEP on a DA42... But the sim is quite light on the controls, I don't think it is meant to be acting like real aircraft.
I confirm that the charts are Jeppesen, not LIDO.
You don't choose your airport, it is assigned for you by the examiner. We all (the group of 4) had the same airport the day of my simulator session. No GPS no Autopilot. And it is indeed friendly atmosphere and mainly basic instrument flying is required to pass. You are allowed to do mistakes if there is no "kiling item" amongst them.
Good luck
!