Hey!

if I am not so serious one there is a 3 month cancellation of all trains due to the recent accident (at least was written so in a news report). So at the moment not at all with Interrail. You can check timings for ferries Santorini to Piräus and then get some bus to Patras or Igoumenitsa. From there are ferries to Italy (Bari, Ancona). Check it out and then find a train from there to Roma. You will definitely be two nights on the road