Business management unlocks as part of the main story. You cant miss it. Also I'd suggest changing ichibans job to demolitionist at lest for a level or two as there is a character skill that you acquire that let's you break down walls in the open world. There is a dungeon a little later where I didn't have this skill and it gated me from some optional paths in there. You wont lose the skill after you acquire it if you change jobs again.