It'll be pretty much impossible to expect EVERYONE to show up EVERYTIME, since RL will show up once in a while. Perhaps we can have people get replaced by the DM occasionally if they can't make the session. On the other hand, we need to be somewhat strict in terms of people simply not being 'in the mood' or failing to report inabilities to attend.
For scheduling, I'd suggest Saturdays during afternoons (North American times) and evenings around Europe.
Also, we'd need, like, a DM.
Hmm, how to set this, let's see.....
Logistics-wise, we'd need about 4-6 players and a DM. In terms of setting a proper schedule, everyone would have conflicting ideals, so perhaps it'd be best to 'impose one (such as the above example) and see the general interest. If we can get the proper requirement, then it's already settled, otherwise we'll see what some people suggest in terms of modifications and adjust accordingly.
For ruleset, I guess I'm most familiar with DnD, but I'd be open to pretty much anything where I could find online resources. In any case, we're limited by the DM. Having a beginning DM might, unfortunately, not be much fun. Someone needs to know the rules of whatever setting we'll be using. So, it'll depend on who's willing to depend and what ruleset they know.