1) We are arriving at Fumicino at Terminal 3 and have 70 minutes to catch our Venice flight from Terminal 1. About how long does it take to make the move?
2) We'll go through customs in Venice, not in Rome, right?
3) Also, we arrive in Rome via Air Canada and our second flight to Venice is on Alitalia, will our luggage be passed on to Venice or do we collect it and take it to Alitalia check-in? The flights were both booked as "one flight" from Air Canada.
Since it is one ticket you are at least somewhat safe. Your luggage will checked through to Venice where you will go through customs. Just a walk through the Green door - nothing to declare. In Rome you will go through immigration, then through security again and on to your Venice flight. The big variable will be the time to get through immigration. Since you have a tight connection they sometimes will allow you to jump the line. Just find one of the uniform people and show them your ticket.
It doesn't take long to get between the terminals, and as Frank said, your luggage will be checked through to Venice. The problem is immigration (passport control), which can be short or lengthy and is impossible to predict in advance.
The good news is that you're all on one ticket, so in the worst case scenario, you'll be put on a later flight to Venice if you miss your scheduled one. The second piece of good news is that there are multiple Alitalia flights a day from FCO to VCE; I just looked for the random date of May 19 and there are 7 on that day.
