Please, figure out and narrow down what the game would focus on. I've basically studied RPG's for too long and if you're going to try and put all the load on the GM to make play interesting, don't even bother looking up a ruleset. If you are going to use a ruleset, realise that it shapes what the game focuses on. If no one decides that, then the ruleset is just a blind shotgun blast in the dark - it might support just stupid, abstract things. You have to guide it to some degree. Just trying to have rolling to hit and armour classes 'n' shit is not guidance, it's just random blasts in the dark. Being real particular on the magic system wont help, unless you figure out what the group will actually be doing and, preferably, enjoying. Figuring out the fiction in minutae does not automatically work out the latter.