It seems like too many stops and not enough enjoyment. IMO it will be very expensive with all these changes of location. I would like to clarify: are you spending 4 nights in London, 3 nights in Amsterdam? This is important because if it is only 3 nights in London, your 4 days is really 2 full plus bits of the others. Counting nights helps establish the pace a bit better. I understand you are trying to fit a lot in, but by bouncing about so much, you spend more time in transit and less time seeing and doing.
I would at least drop Prague and Santorini and add the time to Italy. Fly from AMS to wherever you like in Italy. In Italy you can get that relaxation part without going so far. Try a small town on the Amalfi Coast instead. And if you manage to squeeze out 12 nights in Italy, think 3 locations maximum: Perhaps Venice, Rome and the Amalfi Coast?
Do you have a good guidebook that can answer questions like how to get from A to B? Rick Steves' guides do a great job at that, and more.