Hi Jordan,
The hard part about breeding crab or shrimp (and a lot of other things) is getting them through the larval stage. There has been a lot of research done on this by the aquaculture industry and a Google search on
"Crab Larvae" and
"Shrimp Larvae" will produce tons of information.
Here's an article on culturing some commercial crab species from Alaska:
http://www.afsc.noaa.gov/kodiak/shellfish/cultivation/crabCulturing.htm
And here's one on culturing an ornamental shrimp for the aquarium trade:
http://www.advancedaquarist.com/issues/nov2004/breeder.htm
From what I can see, it's probably not feasible to do this as a means of feeding one or even a dozen octopuses or cuttles.
You mentioned in another post that you are in Washington. If, by that, you happen to mean western Washington State, your easiest solution is to visit a suitable beach at low tide and collect a dozen or so purple shore crabs (Hemigrapsus nudus) which are very common here. You could also put out a shrimp pot (in season of course) from a dock and catch a pretty good supply of 'edible' shrimp (Pandalus spp.) in a few hours. If you're keeping a bimac the water temp you're using wouldn't harm the crabs in the time between their introduction to the tank and their introduction to the octopus. The shrimp may be more sensitive to temp but I'm not sure.
If you can't get to the shore then your best bet for live food is to just bite the bulet and buy it from a vendor such as ShrimpStuff:
http://www.shrimpstuff.com/
Culturally yours,
Alex