Should I buy the romapass now?

Wait. You can also get a RomaPass at any participating museum.

I agree, just wait. You don't want to be locked into a pickup location in case your schedule changes. There are tons of places to pick it up besides the termini or airport. All the sites covered by the pass sell it as well as tourist information points.

Donna

They are available in many places but people have often spoken of being scammed. To be safe, just pick it up at Termini station.

If you pick it up at Termini after getting off the train from the airport (the Leonardo Express), the TI is right next to that track. However, depending on which train car you were in, it may be BEHIND you. We walked all the way down the platform before realizing this, then had to turn around and go back.