Few things regarding the Festival Plaza in S/M are still unclear to me. Why would I want to keep leveling my Plaza? What benefits does it give? What's the max. level? What are Festival Tickets and what do I use them for? Where can I see how many Festival Tickets and Festival Coins I have? And what things can I do with my FC?
In order:
1. Leveling up your plaza gives you access to new facilities.
2. I'm not 100% sure on this, but I believe the max level is 100.
3. Festival Tickets can be received (three daily) and used by talking to the woman in the blue outfit in front of the castle. They let you partake in missions, which are used to raise your Festival Coins.
4. I believe tapping on the pink person shaped icon in the Festival Plaza shows you how many Festival Coins you have. The amount of Festival Tickets can be checked either by talking to the aforementioned lady in the blue dress, or looking into your item bag.
5. You can spend Festival Coins in the various facilities in your Festival Plaza.