Don't try to get mei in lucky stars with so few coupons. I would save your coupons for kage only to get mei then get han and roshi in the jin treasures. Either save your coupons to get items to increase your power or get sailor sakura, a good ninja in water teams that cost roughly 2.8k-3.7k depending on the event.

If you manage to get sailor sakura before level 70, I say focus on han and roshi. If that isn't the case, you might want to try the water meta with mei, gnw tenten, mabui since mabui is a 10-pull common and mei is a 60-pull rare in kage. You might get lucky and get mei in your first 60 pull. Going into events when you;re level 70+ get much harder because people have access to better ninjas, so you can either focus in getting han and roshi while your current team falls behind compared to your peers OR being competitive first then focus on getting roshi+han while you piece sailor sakura fragments.

Focus on developing one team first and since you have sailor and you're half way in getting han. You can still pull seal scrolls as it counts towards to the counter for the super rare in treasures. For example: If you decide to spend 100 this week, all you need to do is spend roughly 100 more in the same treasure before the super rare pops up. Even if you miss this week's seal rebate, two weeks from now another one should be in events but the rebate seals you get are only temporary not permanent. This means you have to spend the temporary seals you get but this week you get permanent seals you keep. The GNW treasure won't come out for awhile so you have enough time to get both han and roshi.