Regarding Iruka- if thats completely new server, investing those<900cp to get 2* iruka is literally the best investment possible, especially since you can get that ammount of coupons without any hussle during first days. In all honesty getting early iruka before others has the same impact as getting super rare in later stages of the game. Otherwise refining and getting 500coin frags from ranked/survival. You can get 3k refining points in a week easily if you buy those and sweep corresponding instances.