Yes I know, that's awfully vague and not at all helpful. But I am really looking forward to this game, and as a fellow game designer and also someone very interested in game economics, I've done much studying on the subject and know what happens when you have a poor economy even in an otherwise decent game *coughflightrisingcough* Even though that game has many game mechanics different from yours, it goes to show what happens when you design a game with the focus on unique mechanics and gives no thought to the economy.
Whats wrong with having an unstable economy?
1. New players are hindered from establishing themselves.
2. Only a handful of players can upset the balance
3. Encourages goldselling and buying
4. Encourages botting
5. May cause players to stop using the currency, and start using their on version. Leaving the economy almost totally out of your hands.
Without having a clearer picture of your game, I can't give specific suggestions to give the economy some stablity, but I can give you guys some guidelines to follow.
1. Keep in mind the sink & faucet principle
a. A Faucet is any time money is created to enter the game(eg. selling to a vendor, completing a quest)
b. A Sink is any time money is taken from the players(eg. buying from vendor)
c. The money entering should stay around the same amount as the leaving per player, a slight increase over time is normal and natural.
2. Use both optional and required sinks. But careful with what you make required and so you don't accidentally make something a chore
a. A optional sink is a farm or bag space upgrade
b. A required sink is a farm tax
3. Have lots of both sinks and faucets. Dynamic if possible so that you can make small adjustments as needed(aka, vendors pay varying prices on items where Price Paid is dependent on a few factors(eg. amount sold in past day,player activity,gold distributed).
4. If you are going to allow a cash shop think carefully on if players can buy items for each other, if cash items are tradable, or if cash currency is tradable. And if so, think how this might affect the market should a player decide to drop $50, $100, or $1,000 at a time and plan accordingly. A player should benefit from cash items, but should never be able to single-handedly modify the price of any item on market no matter how large a purchase.
Some things that are not needed, but would be nice features(you can consider these my suggestions :P):
1. Allow a player to have access to a Single Player option upon character creation. This should allow them to access ALL items of the game through vendors or crafting, but not allow them access to trade with other players.
2. Don't have a system wide auction house. Yes it's convenient, but your targeted player base has already shown they will do what it takes to organize a trade. Auction houses make it easier for botters and other automated ways of working the market. There are many ways to allow easier and safe methods of trading besides auction houses.
3. Allow every player to have a chance to get every item, even if the chance is very, very slim(gachapon machines are good for this, also mod run contests)(paying for the chance to get said item is fine)(having limited items, eg 2 in existence at once, is also fine as long as the holder can't potentially hoard forever)
4. Hard work should equal more pay to be fair, but there should be a rate of diminishing returns to prevent botters and to allow casual players a chance.
What needs to be done during early alpha testing for the economy(tests should last 1week, preferably 1 month)
1. Give players no money to start
2. Give players ALL the money to start(about 1/4th of your cap ought to do it)
3. Give only some players lots of money
4. If you have cash shop money, repeat with the above.
tl;dr - A stable economy makes a game feel fair and fun. Allowing all players, new and old, a fair chance at obtaining the items they need with a decent amount of work and also preventing players from hoarding money, or having too much money and nothing to spend it on.
This is by no means a detailed report on even general game economics. It's a very basic overview that should help point in the right direction

