Is there a texture library in Synfig? And if there isn’t, can we make our own?
There is not any specific texture library using built in filters. You have to make your own or reuse some nice effect form someone else who has shared the files. Bipmap textures are inserted via image import.
Is there any way to use an image as a texture (using the Onto blend method) without having to duplicate and encapsulate the texture layer?