I purchased a Eurail Italy Saverpass. Now i want to reserve seats, am I still required to pay a fee for each time I want to travel within Italy by rail?
Not on the Regionale trains. Those you can ride with your pass. However, there will be a fee on the higher-class trains. The IC train fee is 3E. Most of the Eurostars are 10E. You can easily pay for reservations when you get there.
So on trains from milan to Florence, and Florence to Venice , i need not make reservations till I arrive at station?
Yes. The is always a very remote possibility that a certain train may sell out so it not a bad idea to make a reservation, if convenient, a day or two earlier. Now you finding out why a rail pass in Italy may not be good deal. The regional trains are the slowest but you can just hop on. Be sure to validate your pass for that day PRIOR to boarding.