For a 40 page 30cm square Large Luxurious book, we would recommend between 80 and 120 photos. If you keep the number of pages fixed, the more photos you insert, the smaller the average size of the photos. You can of course have less than 40 pages, or add additional pages. Your choices may be guided by the quality of the photos themselves, and the importance of the book.
For books of smaller dimensions, your page real estate is less, so your photos will obviously be smaller, all other factors being equal. Similarly, if you choose an A3 Large Landscape, you can have the same number of photos but have them larger, or you may wish to make use of the additional space to accommodate more photos.