I just got home from my cruise on the Epic and was in a Studio and can confirm that access to both the studio cabin area and the living room requires your key card.
Also if you are looking to meet people, go to the 5:30 pm daily solo gathering in the Living Room. It probably made the cruise even better for me. The Activity Crew member who hosts the gathering is really good at breaking the ice. Plus she organized a dinner for any of us who were interested as well as have our group attend Legends together.
I really liked the Studio Cabin. It was actually a lot bigger than I imagined with lots of places to store your stuff. It is really great for one person.
One other new thing, you can purchase a day or week pass to Posh (adults only). It's $59 for the week (I don't remember what it was for the day). I bought the week and it was a nice place to get away and relax in nicer loungers and there is also a bar there as well. However, there is a bug in the system, which hopefully they will fix. If you are in a Studio and want Posh access you will need to request a separate card. I found out the hard way if you have Posh access you lose your Studio access and vice versa.
For those that don't know what Posh is, it is the sun deck that was supposed to be exclusive to suite guests during the day and a nightclub in the evening. However, very few of the suite guest were using it, plus NCL realized that because Posh is built over the Penthouses, there could be noise issues if they had loud music in the evening so they nixed the nightclub idea. Because so few people were using it, they decided to open it up to any adults who wish to purchase a pass. It is limited, however I'm not sure how many passes are available. Even doing that it wasn't very busy most of the time. I think one afternoon it was 75% full, but most other times I was up there were only maybe 6 or 7 people there.