At the current moment the game is unwinnable as you can't make it past the first battle against A and B in the Newton Library. This is because the battle is heavily bugged as none of your attacks will do any damage to their two Pawniards and all their attacks against you are instant KOs.
However, I just find out that the Pearls in Sandy Cove respawn if the player sells the Big Pearl at a shop. This is presumably done so that the player does not permanently lock off the Dowsing Machine if the player decides to sell the Big Pearl rather than exchange it for the Machine.
You should probably add more methods of acquiring Big Pearls. You will lock off the Dowsing Machine permanently if you sell the Big Pearl (like I did).
There's no real limit to how many established characters you can use. You just need to make sure that how they are portrayed fits their character in the games.
I believe that mature themes can be done right if they are done the right way, as shown in Reborn. Being dark and edgy for the sake of it, as shown in ZO and Insurgence, should be avoided.
Yes. Games don't need Fakemon to be good. If they are to be implemented they need to be done right, like Uranium, Sage, or Ethereal Gates, for example.