Good rebate events, most are at what you do is you save those resources to certain numbers to get the most out of it.

Cave keys: 1050 or 2100

Refines: 500

Charms: 500

Battle armor: just do as much as you can when the event is happening.

All other rebate events it doesn't matter.

Best events to spend coupons are the ones with both an rng portion and a shop. So best ones are lucky board, lucky stars wheel, and konoha great tree. Other decent ones are fireworks event, great plates to a certain extent, wheel of fortune is okay, and mission mobilization. All other ones are only worth it if you really want a specific item. And also remember to not spend unless you can get the maximum rebate from a fukurokumaru deals (or at least a complete ninja)

You do know how long it takes to get 1400 advanced refines? Putting it mildly would be almost half a year. And in that time, your p1 is going to fall so far behind its not worth it.