1. for now(maybe later no) the best way is to buy magatamas, that's the most worth way for now for few reasons:
there is an option to buy a sealscroll (the one you use to recruit new characters , etc) but people who played on the CN version are saving them to the lv 50 recruit, it's not woth wasting your coupons yet on them(maybe later idk depends on what you need), also they are very expensive so sealscrolls are not worth (125 coupons per one!), whereas you can lv 4 magatamas for that amount of coupons (better value).
2.
refining is supposed to be earned through one of the events (world sage)
the other way is through exchange shop
wasting coupons on buying refine items is a waste of coupons (don't do it ! maybe when you have only one refinement left to complete the max refine).
btw you should check the black merchant every few hours, sometimes they have good things they sell for money ( not real money)
3.
this is one of the items you c*e on the exchange shops...
to enter all the exchange shops you c*e few ways like (enter Ranked Battle/Arena ) and click shop.
you can then go through some different shops, one of them (group shop) is where you use the 'circular stone' you talked about.

4.4 is probably the best till lv 50+ where survival trial and more arena options are given (like 3vs3, 6vs6 ).

5. not bad in the beginning, won't be used late game tho. (not worth upgrading her to 4 stars by using tons of stamina)

6. i am not Water main so i am not proficient in it so idk, kabuto is good because of his every turn heal that he does (you can increase them to the point it's much better than sakura), his 3 star form is better other healers at 3 star. also he creates zombies that are good for battles (because the battle system is not that good in terms of choosing who to attack, they are basically used as good defence instead of attacking your tank (hinata in your case), and since he can do that every few rounds it's really annoying for your opponenet. also, if few characters of yours are dead then the zombies will be stronger and contribute to the battle (not useless).

7. if that's the case then it's probably because you are lower level than avg, try to create a new character in a new server when it just opens and you won't see it .
This post was last edited by Tea at 2016-7-28 05:17 This post was last edited by Tea at 2016-7-28 05:18 This post was last edited by Tea at 2016-7-28 05:20 This post was last edited by Tea at 2016-7-28 05:21

Thanks a lot for all the answers!
Should I spend all my coupons on magatamas right now, or just buy 1-2?

spend all of it unless you're a ninja collector who wanna save 4500 coupon for a 3 star ninja ( event ninja ).. like playboy sasuke or others..

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