IMO, you need at least 2 weeks to cover all of that, just for transportation and getting situated, takes time let alone seeing stuff. Ten years ago we did Thess/Chaldiki in four days, Athens three days and Naxos four days. Travel took a fair bit of time within those days.
In Thess, where there are several museums worth a visit, and it's lovely to walk around the center, sip a cold beverage at any number of cafes, you could jam it in a day but if it's your first stop and you're jet lagged, you may want to do 2-3 so that you have one entire full day there. It will be very hot so may be challenging to do outdoor stuff in the afternoons. If it were me, I wouldn't drive in the city, but not impossible.
I took the train from Thess to Athens but of course, that doesn't help with stops at Meteora and Delphi. It took 4 hours on the train.
I'm currently renting a car from Athens as I was in the Peloponnese and now on Kefalonia. While the car wasn't super expensive, be prepared for $9-11 / gallon of fuel (when converted from liters/euros). Tolls are also adding up. I spent about €18 one way. Ferry was €110 for just me and a compact car.
Look at Matt Barrett's Greece website for lots of extremely helpful info. Click on links on his stie so that he gets a little commission.