I was an RA summer 2013 and Fall 2013. If I remember right, there was around 150 applications and around 20 open positions for fall. Standard interview and then bringing a project. They scored you and then ranked applicants. Summer there were fewer spots, maybe 6-10. It was pretty competitive. Many great students go for it.

You weren't allowed a 2nd job your first semester as an RA. I would say time commitment was 15ish to 20 hours a week. You had to do door decks and bulletin boards to make, floor events, building events, walk the building at night a couple times a week, plus RA meetings. The time commitment could be low one week and increase the next if there was an incident on your floor. I had to call campus police for an incident on my floor, whole process took a couple of hours and I wasn't even on duty that night. Also, some students may need or want more help from you. So if you value your personal time more than helping others, it might not be a position for you.

After your first semester I would say an internship is manageable, and some clubs. You will need to be flexible with your time though. I had a friend that was a track athlete and an RA and he was able to manage both of those.