A single application may include several classes.

Yes

Yes

addition

1. Power of attorney, simply signed. A general power may be used for subsequent filings. 
2. Copy of priority document, if priority is claimed, certified. 
3. 5 prints of the mark for each application 

3 months  

10 years from the filing date

6 months grace period 

Documents required for renewal Power of attorney, simply signed. 

None due

N/A

A mark becomes vulnerable to an action for cancellation if it not was used in the preceding 5 years.