Hey, you can upload either one. We'll accept photographs, digital, even scanned copies. Go buckwild!
With regards to size, the 'standard' size that you get when you open most editors is A4 (210 x 297 millimeters, 8.27 x 11.69 inches). If not, it's one of the options you can select when starting the editor. If you are scanning from a country that uses standard letter, just upload that size and we can sort it out if it gets selected for the book.