My personal experience (sorry, no screenshots):

I got him the first time (I almost never did lucky stars in 3 years of playing, maybe just some 10x) with 5200 coupons;

Next fuku I spent again in lucky stars 30k coupons and didn't got him;

Last fuku I got him again after spending just 800 coupons.

With the obtained stars I always redeemed the power packs.