In the case of the treasures in this area several elements are very characteristic. First of all, in the villa itself you can find one room with some boxes (to enter it use the stairs and the ladder - it is a "cabinet" of Ezio with portraits of his dead victims).  More can be found in the basement of the building.  Go there by the well.
What is more important: to discover some treasures - for example in the church - you need to develop those elements of the city, so start to search only when your estate will be at the maximum state of development.  One of the treasures is in a small cave, which you can enter from the north side of town (under the wall).