you need to clear stage 12 several times to sweep. You can retreat in survival trial without loosing anything so you can try to beat it without any losses. If you loose some of your ninjas, maybe try to set up more team that you can fight with.

You only regenerate a little of your health after each fight. In the beginning a healer is very valueable, so try to use Sakura or Kabuto and try to keep them healthy, so you c*e them in more fights.

I wouldn't say there were common, but i still get them sometimes at stage 9. My stage 12 is almost everytime some awakening material and sometimes there are a couple of fragments (like 2 Jiraya fragments). My server is kinda "new" and i cleared 900~ stages and got like maybe 1x 80 fragments for Zabuza and a couple of times 30 fragments for sound four and got Tayuya almost 5 star because of it.