Ok thanks for all the input. Done a ton of research over the past week, still have more to do. Here's what I'm thinking:

Use points to fly AA MCE(60k/ticket) from LAX to JFK to ROM.

Stay in Rome for a few nights, will try and use points here since hotels are so expensive. I like the intercontinental(looks nice and in a good location). I'll book 1-2 nights for $290/nt and probably sign up for ihg card to pay for 1-2 other nights(50k/night).

Stay in Florence for a couple nights(possible day trip to Pisa, maybe 1-2 nights in Cinqueterre). It seems like Florence is way cheaper than Rome - hotels wise. I might just pay for rooms with cash here.

We're gonna fly Aegean from Rome to Santorini - flight is $200/person - might try and use united points here if it makes sense?? Flight seems kind of expensive for such a short trip.

In Santorini, we'll probably have to pay for a nice place for 2-3 nights. I don't think there's anywhere I can pay with points other than mystique(starwood). We might take a day trip to Naxos or similar island for one day. Then we'll fly back to Rome on Aegean using cash or Aegean pts again.

We'll probably stay in Athens for 2-3 nights, maybe try and use some Starwood pts or something like that there.

For the flight back from Athens to LAX, I'm thinking about doing Turkish airlines. One way trips cost $700 or I could use points. Since Turkish is Star Alliance, I can use my United points to book right? Need to look into how to do this..