Hmm.

Not sure what to advise but if I were you, I will focus on getting a much better Ninja than Sasuke [Rinnegan]. I mean, he's a good unit to have but not the best reliable unit to use as your P1 especially these days where Ninjas like Kisame Hoshigaki [Samehada Fusion Mode] and Kimimaro [Halloween] can nuke him in round 1. As for Kakuzu [Earth Grudge Fear], it will be much better to farm him from events where you can get free points and buy the Explosive Heart Pack, but if you really like him then it is better for you to get him first than Sasuke [Rinnegan]. Thank you.

Hmm.

I have no idea but as long as he's in demand, he will continue appearing in events but don't take my word for it since the decision isn't in my hands. If you really want to get him then you might need to snipe him around in events where his price is decent enough to get and buy it. But I guess, the better thing to do for now is to save up until you get enough coupons for Fukurokumaru's Deal and get more things. Try to plan for special occasions of the game like Chinese New Year and/or Anniversary weeks.