So what's the story on the server? How long has it been active? Will new players spawn in to a world that's already been mined dry and built everywhere? Is the map size unlimited, or are you using a mod like BorderGuard to enforce borders?
It's PvP enabled. Are there any special restrictions on PvP? Is shanking someone in a mine frowned on? What about chests? Are chests protected, or do we get to try and build hidden homes in hillsides to prevent people from stealing everything? What about dismantling other structures players have made? If we built a four-star hotel complete with heated interior swimming pool with an ocean view, would we need to be concerned about someone running around with an axe and hacking apart the west wing for scrap?
How does the economy work? Is the currency a number, or is it a specific kind of item and based around bartering? If it's based around bartering, and it uses a rare material (gold, lapis lazuli, and diamond are the usual suspects due to rarity), wouldn't being able to buy them through donations be kinda unfair?
Is there a spawnpoint changing system? It'd be kinda hard to change your spawnpoint with a bed on a multiplayer server. (It'd be pretty awesome if the shop system could be extended to allow players to create hotels where people get to rent a room with a protected chest and bed for a fee, but I haven't seen any indications that something like that is possible.)