Also is there a best event to get him?

Honestly, probably a around the same as 4* Kakuzu from 0 frags.

The one event I get the most of him from is I think Fireworks event. Since I usually spend on packs for that event (for the purification pill frags).

Hmm.

He was on the previous Lucky Stars Wheel also. This is the event that I think best to get him since while spinning for Stars, you will also get a lot of Training Potions and New Refine Packs. As well as having a chance of getting the Jackpot Ninja.

In my opinion, Lucky Stars is the worst option, cause if you're just going for redeemables, the Training Potions and Refine Packs only prevent you from getting stars, which means, you would get less of what you redeem. Which is why I still suggest to make Lucky Stars work similarly to Konoha Great Tree where we are always granted 1 star every spin.