A little background info might be helpful: I've roleplayed in online games and have some experience with single-player computer games based off of pen & paper game systems (The Dark Eye), and I'm thinking about trying to start a pen & paper game with my boyfriend. He's an experienced pen & paper roleplayer (World of Darkness, The Dark Eye, and I'm sure at least one other system I'm not remembering at the moment).
At the moment there isn't a group set up. While I'm looking at asking around our circle of friends, they would most likely be complete beginners when it comes to roleplaying games.
What I'm looking for in a system
- I'm a bit lazy, so I'd like a system that a) doesn't take a lot of time to learn the rules to, and b) in which you don't spend a whole lot of time calculating things or looking up rules.
- I'd like a system that lends itself to a fantasy, urban fantasy, or possibly sci-fi setting.
- I'd also like for the system to be easily portable to different settings, so that if we wanted to run a game in, say, the Harry Potter universe, and then switch to Middle Earth depending on player preference and familiarity, we could do that with minimal changes and few house rules.
- I'm heavily into roleplaying, not roll-hack-and-slash for gear, and I'm looking for a system that supports that with a plethora of non-combat skills and a focus on interactions, so I can create more "normal people" characters and not "Me strong adventurer! Me bash everything!"-like characters without being at any serious disadvantage.
- The system should lend itself well to both one-shots, campaigns, and one-on-one play. If we're starting with people in the group new to RPGs, a few one-shots would probably be best for them to get a "feel" for roleplaying, but I prefer more in-depth campaigns, and I wouldn't want to force a system switch on them for that.
- Since I'm not sure how much time any potential group members would be able to commit I'd like a system that would lend itself to a bit more flexibility as far as player attendance goes.
For instance, one person would be interested, but she lives in another city and keeps busy, so her attendance would most likely be spotty and it wouldn't be much fun for her if her character ended up vastly under-powered because she couldn't make several sessions. In general our groups of friends consists of young adults with busy lives who most likely wouldn't be able to make every session--not just this one person. (Maybe this is a playstyle and campaign issue, I'm not sure.)
- Ideally I'm looking for a system without the need for a GM (to support a "not everyone has to be there all the time" group dynamic).
Is there a particular system you would recommend that meets what I'm looking for?
If there's any other information I can add to help you mentally narrow down what I'm looking for, please let me know what.
(The original question also included questions on how to handle the group dynamics of one-on-one with possibly adding in more players. I edited it to conform to Stack Exchange standards of clarity and single-topic focus, but I appreciate the answers that have already been posted!)