I always draw my quilts out on graph paper. How large will the pictures be? This will determine the size of your 9 patch blocks. How large a 9 patch were you thinking of? Are you going to put a border on it? For example 4 12inch blocks across would make 48inches. A 3 inch border would make 54inch width. A 12inch finished size 9 patch uses 4inch blocks, finished size. A row of 3 15inch finished blocks would finish at 45inches and you would need 4.5 inch border to make 54inches. All these decisions and things to figure out. I love doing this stuff. If you want a picture in the center, 3 blocks across would work better. 5 blocks down would work with a pic in the center. That would finish at 75 inches though. Can be complicated.
Have I thoroughly confused you now? Sorry I got so detailed but I like planning quilts.