"We want to take the the train for as much of this trip as possible."Good news: you can do that entire trip by train, no rental car needed (and no rental car recommended, the traffic in downtown Venice is really bad! :). Suggest you use this website http://bahn.hafas.de/bin/query.exe/en to get a general idea of the schedules, # of connections, and routing (through Milan on both legs). Country names not needed, dates not needed (just pick a date next week, during the week or weekend as applicable to your trip), input Paris to Varenna-Esino, arbitrarily input 0600 as the time so you get all the schedules for the day. After you've done the above, then repeat the process for Varenna-Esino to Venezia Santa Lucia (best to spell it exactly that way on the website). You aren't going to use this website to buy tickets, just to get an idea of what the schedules will be in August (should be similar to what you're seeing now).After you've done the above, if you have follow up questions, don't hesitate to post back here.