Fly into rome on friday morning stay until sunday morning head to cinque terra(been there before), leave for tuscany on tuesday(maybe siena or assisi) head back to rome on thursday night and fly out on saturday night. Is this too much or a nice mix of big city, roman history, small town, and beach time

It's a lot of time on the road or rail. If you've been to Cinque Terre before, why are you trying to shoe-horn it into this trip? Why not just Rome and a couple of days in Tuscany?

Very hectic organisation...
No need of a car in Cinque Terre, in fact it's more of a nuisance...

If this is your first time in Rome, then stay in Rome for 4 or 5 days and make a 2/3-day excursion by train to Assisi or Siena, or rent a car for that period.

It does seem like a lot of traveling for a short trip.
Questions:
Are you driving or relying on public transportation?
When are you going?
Is this your first visit to Rome and Tuscany?

Assisi is in Umbria, not Tuscany.

You said you were trying to include small town(s) in the mix. I didn't notice any small town on your list of places, unless you are staying in a small town in the Cinque Terre.

In general, I think you're covering far too much distance in too short a time. If you want to combine some beach time with visits to Rome and Siena, why not pick some beach area(s) in Lazio or Tuscany?

I agree--3 destinations is one too many for your time. I would do 4 nites in Rome--perhaps at the end--and spend the rest in Tuscany. Train to Chiusi to get your car for Tuscany.