@liketraveling I'm getting ready to leave for Barcelona and was looking at the metro information. I wasn't sure if you had looked into yet or not, but you can go to holabarcelona.com and get visitor passes that are good for certain periods of time (2,3,4,5 days). They are good on all public transportation for unlimited use. If you buy them online, you get a discount. They will email you a code to use at the ticketing machines, so you can pick them up when you arrive. It includes transportation to and from the airport, which the regular single ticket journeys do not.
We got to Barcelona a few days ago and I love it here! The metro ride from the train was the way to go for us. It was very easy to navigate and the train station was empty when we got there. It took about an hour for us to get to our hotel. If you are traveling with kids, I highly recommend the Mission:Barcelona scavenger hunt book. You can find it on amazon.