how im planning out to layout my photographs (practice)

I used old photos that are un cropped and tried making a square and i found out it is slightly impossible to do, as i don't want to crop my images also i would have different sizes of cropping so i would have some irregular shapes, so i have decided to overcome the idea of a 'perfect' square and lay out my photo like this 3X4 (all landscape). so then when i edit my pictures i will use alt + cmd + I and the resize the image from cm to inches 4.18 X 3.2  dpi 300 (cm) and then copy the image and paste it on a new document size of 6 X 6" and 300dpi (cm) stack them into a full picture, I will use this layout through out my book.