The book is 30cm width and 20cm height. Some pages can be unfolded, so the biggest panorama inside this book could be potentially 90 cm x 20 cm.
300dpi with that dimension is around 10000 pixels in width x 2400 pixels in height.
Now, the more the better, don't hesitate to provide more
BTW : for page commodity of page layout, we may crop some panoramas. So if we have more quality, it's better. About cropping, of course, we'll respect the composition and spirit of the picture, it's just to be able to fit the panorama is some aspect ratio, or because it has 5% top much in width or height, sometime like that. I hope you can understand this fact of page layout to fit in everything in a well balanced way.
I would recommend you to use jpg and tiff format only. If you have a profiled screen and want an accurate colorimetry, please flatten the profile in the image to a standard profile like adobe RGB 1998 ( prophoto should be avoided probably because it's too extended ).
About the number of panorama you can provide : Don't hesitate to provide many. The number of panorama of everyone we will put in the book will depend on the success of this project. If 20 users participate, you'll get a lot of pages each. If 200 users participate, it will be around 1 page / user, etc. So yes, for the moment, no limit in the number of panorama you can provide. In fact, the panobook interface allows you to upload / delete panorama as long as it is opens. So you can put 10, 15 there for the moment. One or 2 weeks before the dead line ( end august ), we'll have a good estimation of the number of panoramas uploaded and perhaps we will ask you to make a final choice of 3 panoramas for example, or more, or less depending on the success.