I don't mind this idea, but I think you are going about it the wrong way, this should not be a class at all, as it would do nothing relevant (what would its tool be and why would you even need to have a tool?). This is OK as just content that any class can do though, a side quest to learn about the economy and how the MB works might be cool to educate people. As for the minion, I will say that it is fine so long as it only gives around 400gil an hour (makes it equivalent to retainers), that might not sound like much, but it's free gil that is balanced with equivalent content