Be aware of the Emission Trade Scheme in place in Europe, that MIGHT affect you. (I donīt know honestly, being German we are 'part of it')
Be aware of slot regulations, there are both airport slots at some places and the infamous Eurocontrol generated airways slots.
Make sure your handler requests the airport slots for you, in Europe a lot of the handlers donīt think 'real' handling is their part of the equation... a lot of them think, taking you from and to your airplane plus generating huge bills is their part.