You probably X'd it by accident x'D - I've noticed a lot of people are doing that lately.
1. Yes - Only one path, since it's kind of impossible to be in two places at once - right? x'D
2. Yes - As for next 'Arc' Typically each month has an "Arc" of sorts with 4-5 parts, just like before :'3 (with the exception of october - november, which were slammed together thanks to Chunin exams.)
3. No, because that gives an advantage to Multi character members (since to maximize opportunity each char should do 2 missions anyway - so theoretically, you could just do two each for each character)
The point of the bonus is to reward people who do extra work. It's per character :3 so if you did two missions with Michio and the other two with Dairou, neither would get a bonus - but if Michio did all four or five, he'd get a bonus.