How do you plan on distributing the market cap fairly? Will the first thousand people to join be given a free check, or do you have something else in mind? How do you intend on dealing with lost money, for example somebody could spend a lot of time becoming very wealthy then bore of the game and stop playing or even as an extreme have their key revoked. Also in this pool is everybody you will ever ban from the server.
I assume you're taking a classical point of view on the economics on this server, not Keynesian. If the server suffers from cost-push inflation, how do you plan on keeping the server fun for new players who will have to work much much harder to make any usable amount of income? How would you deal with collusion? Monopolies?
Will there be a way to force users to sign contracts to make deals legally enforceable? For example, if one party wanted to act as a bank and loan cash to people to start a business, what's to stop people from taking the money and running? If you did implement some kind of loan system, how would you deal with loan sharks charging insane interest rates? A hard limit? Would there be a bankruptcy system where if people fail to meet the terms of their loan contract and are unable to pay a payment on their loan, will they be jailed or can they declare bankruptcy to avoid this?
Would it be possible for people to create multi-person businesses with a pay structure? For example, a shop where you can be hired as a cashier and be paid some percentage of profit when you work? If so, would there be a minimum wage? If not, why not? Businesses could push this from a hunter-gatherer type game to almost a real city. What's to stop admins from making random, sweeping rules that could severely damage the health of the economy?
Will there be some system of governing and law enactment? Will users be able to run for office to create new laws, or will the laws be set by admins arbitrarily? Will admins be able to make retroactive rules and punish people for doing things that were not at the time illegal?
Will there be income taxes? Or will government agencies run off income they have to make themselves, for example would police take and split the net worth of a criminal they capture?
For that matter, what would prevent police corruption? Would it be within the rules to allow criminals to bribe officers?
I think that's enough questions for now. I don't want to overwhelm you.