I can't decide which train pass to get, if one at all

I should clarify, I will be traveling in between those dates.

I start for 3 days in Rome, then head to Florence, Pisa, CT, Venice. Over night train to Viena, then Prague, Munich, Geneva, Barcelona, Paris, Rome.

Ck www.ricksteves.com then under railpasses.
There is a good guide to see if it makes sense or not. All the detail and requirementrs are posted there for you to use at no charge.

This website might give you some advice:
http://www.railsaver.com/

If you don't buy a Pass prior to landing in Europe, you could just buy point to point tickets at the station. If you want a Pass, that must be bought in the US, prior to deparure, either on-line or with a travel agency, which I would avoid because there will be a $ 30 handling fee.

If you take a night train, you don't necessarily need a couchette or a sleeper...for those you have to book reservations. I don't do that, only once in the times I've taken a night train. You don't need a reservation to sit in the general seating area on a night train unless you're taking a TGV night train.

What I do on a night train going between Germany and France is to sit in the seating area and sleep upright. If you can do that easily, all the better.
I have no problems falling asleep while sitting upright
Since they were not TGV trains, I could just hop on with a Pass and find any unreserved seat. It all depends on how much flexibility you want as opposed to getting yout money's worth on the Pass.

Go to the national rail websites for the countries you are visiting and figure out the cost of point-to-point tickets vs. price of rail pass + supplements.

Like someone said, unless you ride in the general upright seating area on a night train, you will have to pay a supplement (about 40EUR in Germany, probably comparable elsewhere).

High speed trains also require supplements. For example, the express bus/ICE train combo from Prague to Munich requires reservations. There are regional trains without reservations going that route, but they do take at least an hour longer.

A lot of people on this board has figured out that it's just as good to buy point to point tickets. Remember, even if you have a rail pass a lot of times you will need reservation and that cost is not included in the rail pass so you will have an extra cost.

I don't buy passes because I keep my travel legs short. Point to point for a short trip is much cheaper.

For overnight trains, long legs, a pass may be the better way to go, you will have to price your legs and see.