I play on a silver account, and ive gotten a pretty good feel for what is and isnt allowed. The deal with the broker is pretty easy. Bronze accounts(absolutely free) need to use broker tokens(purchased from the marketplace 10 tokens for 50 station cash) to buy or sell from the broker. Silver accounts(one time 500 station cash upgrade) can buy from the broker, but cant sell unless they get the tokens. Gold accounts dont worry about any of this. Bronze accounts can only upgrade their spells to tier 3(adept), while silver gets tier 4(expert), and gold gets tier 5(master) - they sell spell unlockers to let you go beyond your current limit(marketplace 5 unlockers for 150 station cash). Bronze can only wear treasured or handcrafted gear, silver get mastercrafted, gold get legendary and fabled(marketplace 5 item unlockers for 150 station cash lets anyone wear gear appropriate for their class and level). The money limit is the most annoying one. Bronze accounts can only have 5gold per character level. Silver get up to 20 gold per level. Gold accounts have no money limit. Bronze and silver accounts have fixed AA sliders, gold accounts have adjustability. Bronze and silver accounts are limited to 4 races and 8 classes(class unlockers are sold individually, races come in sets of 3 - these unlockers are 750 station cash), gold accounts can make whatever. If memmory serves, bronze gets 2 character slots, silver is 4, and gold is 7(more can be purchased by anyone on the marketplace, 1 slot 1000 station cash). Silver gets you a couple extra bag slots and bankslots over bronze(i dont remember the exact number here), gold gets you a LOT more(2 bags, something like 2 dozen extra bank slots) - again, theres an unlocker for this on the marketplace(sold individually, forget the price). I also remember the upgrade from bronze to silver unlocking all the chat channels(bronze only get like 4 or 5 of them), which is a big help. Its hard to ask for help when you arent allowed to talk in most of the chat channels.
There actually is a matrix on the official website that explains all this. Id link to it, but their site is down along with the rest of the game for maintanence. Maybe look for a "free to play" matrix when you can go check that out again?