Hard to say, event ninjas now matter too much. I am barely using treasure ninjas. Imho what you should do, since you have gaara, is to gather coupons and piece or jonin minato as zathroth told you or angel god konan. In both the cases ay3rd is a good support 4th ninja if you use wind main.

Going for gnw super rares is a very long journey for a f2p.

Not even one of them is a gnw super rare. That said here i play since over two years, i am notca f2p and i still don't own hashirama.