1. You save them for events later on for rare ninjas or for refining.

2. YES! refining is one of the most important part of increasing your winning rate during pvp, having a high refining level c*low you to beat players with power that is a few thousands higher than you. Why? because the attribute - initiative - determines the order in which you attack. The description it gives on here is very vague, and people might be confused of what it does. Basically having a higher initiative will allow you to attack before your opponent, and the reason why is this so important is that for instance, if you use your mystery that causes immobility to your opponent, you can immobilize them before they use their mystery that might kill you in one hit.

So yes, refine all of them.

3. they are basically tokens that you use to exchange for good in the shops

4. upgrade those that are usable for the long term, like hinata's pretty good for ninja exams even in level 100s.

5. yes hinata is good.

6. kabuto is a good healer

7. try asking people in your group to help