Firstly the diodes D1-D4 are unnecessary. They may even cause problems due to the voltage drop across them. However you should put flyback diodes across the relay coils as explained in the article.
I just checked my 60D and the current that flows through the focus and shutter circuits seems to be less than 100uA. So even some small reed relays will do the job.
Optoisolators aren't really needed here since the relays are isolating your circuitry from the camera.