Yeah but i wonder about other missions. and are some other story missions going to be online?
Odds are small side-quests, but SEGA would be idiotic to make players who can't go online have to be online for the full main story.
I meant like other stories.
Once again, doubtful. It would be unfair to the offline players if they missed any signifigant stories.
I see. Your probably right.
Maybe the missions could tie in with events from the story mode but with a different perspective. Im not sure how the story mode pans out but for example, the guardians are performing a certain mission. From what I can gather the guardians are like a big army so maybe some of the story mode missions could be replayed with your online character. Maybe securing areas or mopping up after Ethan. Im just speculating here it's just some random maybes off the top of my cranium.

The Kevwin
For your fourth question... You may have up to 4 different characters saved in extra mode, so I assume it's the same online.
Online its 4 and offline in extra mode you can have 5 saves.
No, it's 4 for Extra Mode as well. On PC version at least. It's 4, 4, and 4. 4 Story, 4 Extra, 4 Online.
Oh i thought for sure i had 5 saves on extra but i could of been wrong.