Putting It All Together

Here's how I did it:
1) Open each photo and resize it to 600 pixels high. (image > image size)
2) Change canvas (image > canvas size) size and use the "relative" checkbox to add 200 pixels in width and height.  Canvas extension color is background color: white.
3) Make a new document (height 600 pixels, width whatever you guess, mine is 2600 pixels.
4) Copy your first letter (select > all, and edit > copy) and paste it into your new document. (edit > paste)
5) Press v and move your first letter until it is located where you want.
6) Repeat steps 4 and 5 until you have all of your letters where you want them. You can always change the canvas size to make it wider.
7) Change the canvas size to make the whole thing 800 pixels high. This creates the white border you want around the top and bottom of the image.