A) Arduino programmers usually avoid pins 0 and 1 because of the complications caused by sharing with the Serial port. Please change the pins that are used for CAMERA and SHUTTER.
B) You have numbered states already. That is great! I would suggest that the numbers go 100, 200, 300, etc. so that additional states can easily be added in-between, but it is not important.
C) Some aspects of your requirements are unclear to me. For example, what happens if the shutter gets triggered after step 4 in the loop when the CAMERA output is LOW but step 1 of the interruption requirements says that CAMERA should still be HIGH? What happens after step 4 in the loop? Step 1? But this would mean that CAMERA would go LOW only for microseconds. Is that your intent?
D) If it were up to me, I would use different numbers in the loop and in the interruption just to avoid confusion, but it is not important.