Many questions about Venice in this period, I'm happ.
I will post some of the best sources I know, this is just a few of the one that come to my mind but there are more and I will try to update it as soon as I find or remember about others.
Most of the sources are from 1400/1500 and are in Italian, but there are some in Latin. If you don't know Italian it will be hard to read any primary sources (but hey a good excuse to learn a new language).
The first links I will post are all to the collection of Eugenio Alberi, this is the biggest and most complete collection of relations of Venetian Senators, you will learn a lot about the opinions of important Venetian "Patrizi", Venice relation with other Italian states, Venice relation with States outside of Italy and so on. This collection is mostly about "foreign politics" or geopolitics and not about internal issues of already conquered territories. A lot of the relation are from 1500 forward, but I am pretty sure there are lot of them that are from mid 1400 and forward.
I have linked a few links but there are many other books from Alberi you can find in the same directory.
https://books.google.it/books?id=hSZdUaAeOOIC&printsec=frontcover#v=onepage&q&f=false
https://books.google.it/books?id=mycavihYYqgC&source=gbs_similarbooks
https://books.google.it/books?id=JbyXg_2dS2AC&printsec=frontcover#v=onepage&q&f=false
https://books.google.it/books?id=mXziOkxVxV0C&printsec=frontcover#v=onepage&q&f=false
https://books.google.it/books?id=al3HS4kM9kAC&printsec=frontcover#v=onepage&q&f=false
About overseen territories, there are some traties written by Venetian functionaries that supervised Croatia, and other parts of the eastern adriatic coast. This collection is from Šime Ljubić and you will be able to learn a lot of stuff, like uses and costumes as perceived by the Venetian, how the territory was overseen and controlled and so on. Same thing here there are some relations from early and mid 1400 and some from early 1500.
https://books.google.com.sb/books?id=Vs_rxjds7vMC&printsec=frontcover#v=onepage&q&f=false
Other collections of Venetian sources are the one from Leopold Von Ranke, that made a collection of the Venetian relation with the papacy and the administration of Greece.
I will try to update you on on non italian sources, and earlier sources, but I need to have a think.