You want A4 Half Fold brochure? You ok with .indd file or only .psd?

I see that there are about 45 total items to be listed, if 15 items are shown per page (first one is the cover ?), four pages will be completed... Is it right ?

That would work, but it doesn't have to specifically be 15 per page. Some can be grouped together to save space.

4 pages of 8.5" x 11"
so back to back 11" x 17"

only .psd, sorry :(