A better way than adding each image as its own tileset, is to add an “image collection” tileset and add all your images there:
There is currently no real nice way of centering your coin on a tile. Your options are basically:
- Put the coin in its own tileset and use the tileset’s “drawing offset” property to shift it to the center.
- Expand the coin’s graphic to be large enough to allow placing the coin in the center of a tile.
- Use an object layer to place your coins, then you can position them freely.
The second approach allows the coin to still be part of your single tileset, and it should actually not waste any texture space since the transparent pixels can be automatically cropped by TexturePacker.