Do not fly Ryanair - total false economy - takes hours and hours out of your trip and doesn't save that much money once you've paid for the coach. (plus there is the fear that the coach will be full and you will miss your flight back) Fly to the actual Barcelona airport and you are practically on the metro already.
Do get a 10-trip ticket for the metro, it's very easy to use, fast & reliable.
I have stayed here in the Hosteria Grau twice. It is just off the Ramblas, in the centre of everything. Lots of bars and restaurants nearby. It gets quite good Tripadvisor reviews too. We flew Easyjet and got the metro from the airport.