As free to play, you should gather as much as you can.... yet if you take too much time gathering you wont be getting scrolls from events cause you dont have good ninjas and you cant win anything. I would go for a 200 pull to get the best from it.

Regarding good water lines, you could use Roshi along 2 healers (main and sailor sakura) + Mei ..... or if you go kage treasure and pull Mei and Chojuro you can add Ao and make a line as well.... If you get Mei and Mabui from kage, you can get GNW 1010 and make the traditional cancer line as well...

The thing is: if you are pulling from kage treasure, your pulls will decide what class you will follow, we cant be sure you will pull mei and keep water.... I would go for at least 1 kage pull and decide the future based on what I got.

the thing is : both matsuri and sage are cross server events and other players may be ahead of you in terms of ninja.... if you feel comfortable its fine! Do the pulls during a rebate event and get the best from it.... as I`ve said, I would pull from kage and based on what I got I would decide my main class and what shall be plan after