The point of specifying individual bots is only to customize the Disallow rules per robot, so you should customize the robots.txt as you feel best
Additionally, regarding the subfolder location of your site, you will need to place the robots.txt in your site root, and then prepend the /shop path, as you already mentioned.
Here's a couple of helpful URLs regarding robots.txt:
http://www.freefind.com/library/howto/robots/
http://javascriptkit.com/howto/robots.shtml