Re: T10 3 Zone integrated travel ticket
It is Zone 4 for Rodalies only tickets. For ATM tickets is Zone 3.
Re: 5am aerobus plaza Catalunya to airport
Lots of things to consider: checking luggage? Flying in or out Schengen? For your tranquility, use N16, N17 and N18 night bus services.
Re: Barcelona Airport - passengers needing special assistance
It is also good to fill out this form, it helps make things easier for Aena: https://wwwssl.aena.es/pmr/inicio?lang=en
Re: Renfe train
Any train on Platform 2 at Plaça Catalunya Rodalies station will work. They run every 3-5 min. They are free of charge with your AVE ticket, using the Combinado...
Re: validations of metro ticket cards
If you are changing systems: eg Metro to Rodalies, then you will revalidate the ticket, as you will find gates that won't open unless you validate.
Re: train from Sitges to Barcelona
You can't book commuter trains, the same way you wouldn't prebook a tube train. Just turn up and go, it's fast: rodalies.gencat.cat