OK, first thing is that you probably don't have time to do all of this in a two-week trip. You need to count the amount of nights you'll be in Italy, and figure that every change in location is going to kill 1/2 a day or more. Some of your locations are best done as day trips (e.g. Pisa from Florence) and others demand some dedicated time as they offer so much to see.
Secondly, you do not have to drive to any of them; take trains/buses. If you're basing these destinations on an RS tour itinerary, that's more difficult to do on one's own without private transport waiting for you and guides at hand; much too rushed.
My husband and I do travel Italy independently (so far, and we haven't driven anywhere) and love it that way but it's not for everyone. If you don't like the planning/research process or would feel too insecure without escorts, then a tour may be a good choice for you.
Spend some time with some guidebooks and ask lots of question here on the forums! You have lots of time to put this trip together, and the more you know, the better you'll be able to make the best decision for YOU. :O)
Need ideas of where to fly into, Venice or Rome
Flying into one city and out of another eliminates backtracking so that's always a good idea. Venice is best flown into versus out of as flights to the U.S. tend to leave early enough to cause (expensive) complications with transit to the airport.