I won't recommend holding for kage, sage is worth doing and leveling from 70 to 80 literally takes months (70 is when sage opens, 80 for kage). Quite frankly, the amount of extra stuff you can get from sage world battle field in the months in between will outweight a bit of kage pull over sage.
Granted, traitor just got nerfed, so pulling that would be a *er, but Ao and sage naruto are both good enough to pull for.
Some of the pain would be worth it too, but that treasure have too much variance.

Magatama: make sure you make the as EVEN as possible, across all 20 slots (5 per equipment, 4 per equipment type on 4 chars). Of course, feel free to put the highest one on the most effective ninja, but don't go making lv 4 magatamas when you still have empty slots or slots with lv 2 magatamas. As for ninja exam where you get it, remember you get to try as many times as you want to grind pass a level (and once you pass it, you can sweep it so never have to grind again). This can come in handy, as you can literally try again and again for the one fight where everything goes right (your chance to blah blah hits all proc, theirs don't). Furthermore, make sure you carefully study the opponent and come up with a counterplan, the enemy don't change, nor does their behavior, generally it's fairly easy to interrupt/acupuncture them.

Make you sure you do survival, make sure you do it right, use a high sustain team with heals and/or shield for the first 9 nodes so that you don't lose anything on those easy fights. Then, you will have character to spare to grind pass the harder nodes.

Equipment improvement material, the scroll aside, can be farmed from plot instance. Hover your mouse over the material required will show a "!" mark on the corner, click it and it will tell you which instance you can get them from. Generally speaking, those are the best expenditure of stamina. Passing all the elite instance ONCE is good, but do NOT farm them all. Instead, pick and choose which ninja you think you might use for a long time, and farm those only. As far as the ninja that drops from elite instance, the most useful ones are kimimaro, guy, neji, hinata, sasuke, karin, kurenai, not necessarily in that order and differs by main and purpose. most of the others are completely useless.

Make sure the ninjas you use the most are polished: awakened, mooded, cultivated and farm their fragment to upgrade their stars. (note you can farm awaken mat on the awaken interface same as you do the equipment upgrade mats)

Make sure you join every event, even if you don't do well in them. That means fox, masuri, sage world battle field and great ninja war. Free reward is always good. You SHOULD have a dedicated fox team, as the mechanic is quite different from PvP, a dedicated team can easily double your damage and thus reward or even more.

And finally, just go around clicking every *on to check out every feature there is, completionist is the way to go, there are a LOT of different activity you can do to gain power.