I'm trying to create a photostory project with photos from a file, and I can't see all of them. Is there a limit to the number of photos you can put in a project, and/or is there a limit to the size of a project?
First, please read this post and give us ALL the information requested there.
Second, depending on the hardware your computer runs (hence the request for more details) I can think of the only limit to the number of photos you can use in a project being caused by whatever medium you intend to use to store the export.
When you say
I can't see all of them
I assume you mean you cannot see them on the Timeline? The "length" of it which is visible on your computer screen is limited by your screen size, but this does not limit the actual total number of images you can use. The timeline can "extend" beyond the edge of your screen.