Adv. refines and cave keys. I recommend you buy them now, because there is a possibility that cave key rebate will change (in China you need over 5000 keys for ultimate essence). Bond mysteries can wait, unless you use Jonin Minato.

Buying adv. thread is just not optimal unless your'e finished with rune stones and treasure tools. It is the most overpriced item in the game for the amount of power it brings (maybe on par with purification breakthrough pill). Unless you want to have cool looking battle armor :)

Yeah, but if you use Itachi anbu his bond mystery won't usually impact much (unless you have Madara), because you will use it round 3 or at the end of round 2 (after you get chakra from calm mind)... Usually fights are decided before you get a chance to use his mystery (at least in standard teams, where Shisui is pos1 ninja). Minato's bond is kinda essential though (and Edo Tobirama's, if you have Edo Hashi...)

And to activate bond mystery you only need to have total lvl 25 assist for that one ninja (you don't need to get Shisui's assist to 25 in order to activate Itachi's bond mystery). Read more:

https://forum-narutoen.oasgames.com/page/show-post-33705-1.html

https://forum-narutoen.oasgames.com/page/show-post-33417-1.html

https://forum-narutoen.oasgames.com/page/show-post-33393-1.html