Keep stacking if you are unsure, you c*ways decide later. Even if you overstack to 900 or more, seal rebates are every 2 weeks so you will use them eventually. This way youll see how meta might shape in following months and decide what is better to pull. At this point super rares in gnw and kage are irrevelant as top meta teams (even more since you have sosp), so whether you have X treasure SR sooner or later it virtually makes no difference. Btw you should only use x300 rebates anyway to gain most benefits, so either waiy you should wait.

Yes it is, for edo hashirama.

Btw, kurama works better than six paths against some lineups (overall heavy dodging teams) since is granted to deliver 10 combos to the target you select and the boost to combo is higher (+80% vs +45%) don't forget also that his standard attack delivers ignition too. Obviously, in general, six paths is better, but not always.