If so how many can be included in a .pclx Pencil2D project file?
There is practically no limit on the number of layers you can have in a project. However, it will take longer to render a frame for each layer you add, so it is largely dependent on what your computer hardware is capable of handling, how long you are willing to wait for each frame to load, and how many layers you can actual manage as a user.
Thank you for your prompt answer.