I can probably be of help here. My partner/girlfriend/missus of 8 years is from Barcelona. She's been living with me in London for 6 years, I've been many times and I'll probably end up living there at some point.
Great weather, October will still be nice and you can expect 70-80 degrees. Rain is unlikely but the climate in general's up the spout lately so who knows..
Great food, seriously, these guys know how to cook, eat where the locals eat, you won't be disappointed. All cities have their shitty tourist traps but I've never had a bad meal there.
I can probably speak with Marina and ask for her advice on where to stay but the good thing is that its not a massive city, has a beach, a port, a little mountain with a castle/fort and you can get round really easily by metro, tram or foot.
Young people are pretty cool and they have a very family-orientated social culture, and are very proud of their culture and language, separate from spain.
Give me a shout if you need any info Bona nit.