Draft Tour Route For Upcoming Europe Trip

Which is a better to place to transit if we are flying to Venice from Singapore? Is it Amsterdam, Dubai or Istanbul?

I'm currently drafting the tour route & base on my first draft, the Days distribution are as follow. Will it be too rush? Really need opinion on this major trip. Any help is greatly appreciated.

Italy Section
Venice - 3 Days
Florence & Pisa - 3 Days
Rome & Vatican City - 4 Days

Greece Section
Athens - 4 Days
Santorini - 2 Days