i think only you can really decide if it's a good idea....
but you have to think about your distance from water, how you'll get crabs, how often you'll get crabs, will you sell them live or steamed, financially how will you do it, how many crabs you will need per week, is there a market for crabs where you live, will this be a year round thing or just a spring/summer/fall thing....
lots of questions to be answered...
Thats right,supply and demand is the first problem he has to solve. being far of the normal routs you might want to look at getting cooked crabs shiped to you