I know next to nothing about the Minecraft setting, but I guess it doesn't really matter if you call a monster creeper, orc, grue or whatever. Having the wilderness full of monsters will encourage the players to group together in towns rather than going solo all the time.
Anyway, help with developing the game system is more than welcome. I guess it's easiest if I just post everything that I've came up with so far. Everything is subject to change in case of better ideas popping up. Brace for wall of half-finished rules...
A new player character starts with 10 HP, and the player can choose any skills for the character that aren't too generic (Warrior is too broad, Swordsman is fine). The player can assign 10 skill points to the character's skills. Each skill can have a maximum of 4 points. The skill points can also be spent to increase the character's HP.
Skill checks are made by the GM using the Roll to Dodge rules. The skill value is added to the roll, which can go up to 10, with increasingly epic successes. Every skill has its own result table, made by the GM when needed, and then preserved to be used again when necessary.
The world is divide into a large number of smaller regions. Every region has a number of attributes that are kept secret from the players (unless they figure them out with an appropriate skill). Each attribute is randomly assigned at the start of the game.
-Savagery (probability of being attacked while in the region) 1d10+5
-Animals (availability of hunting game) 1d100
-Trees 1d100 (used for building/crafting)
-Soil nutrition (used for farming) 1d100+50
-Gold ore 1d100-90 (melt into gold bars, then mint gold coins)
-Iron ore 1d100-70 (melt into iron bars, then forge stuff)
-Flux stone (combined with iron to make steel) 1d100-70
-Stone 1d100+100 (used for building/crafting)
-Monster lairs 1d3 (decides how many active monsters there can be in a region)
Savagery, animals, trees and soil nutrition increase by 1 on any day that they are not reduced by something else, unless they have already been reduced to zero.
Each character gets up to three actions every day. A player can post new actions for their character as soon as the GM has posted the results of the previous actions. The GM will ideally post results once per day. At this time, region attribute increases and other world stuff is handled.
Any character that takes action must eat a food ration the same day or lose 2 HP. This happens automatically as long as the character has food rations in their inventory. If the character has lost any HP, they will regain 1 HP from eating a food ration.
The following things consume one of your actions:
-Moving to an adjacent region
-Building a house, or adding rooms to an existing house
-Going into a monster lair
The following things are free:
-Declaring oneself the ruler of a region
-Placing and receiving bounties on people/monsters
-Setting, paying and collecting taxes, wages, and other types of payment
Houses can be built with wooden logs. Each room in a house takes 3 logs or 3 stones to build. A room can be made useful by adding furniture (the necessary components for the furniture are shown in parentheses).
Bedroom: Bed (1 log)
Throne room: Throne (1 log)
Shop: Desk (1 log)
Mill: Millstone (1 stone)
Bakery: Oven (1 stone)
Smelter: Furnace (1 stone)
Forge: Furnace (1 stone)
Coal furnace: Furnace (1 stone)
If you end your turn in a region with a bedroom that you own or have paid for, you will regain 1 HP from sleeping.
You can declare yourself the ruler of a region if you own a throne room in it, and the region does not already have a ruler. It might be wise to win the support of the inhabitants first to avoid instant civil war.
Once you are the ruler of a region, you can set taxes in it. The tax can be any percentile that can be divided by 5 - 5%, 10%, 15% and so on. Anyone in your region that earns money must pay this share of the money to you. But they can specify that they refuse to pay the tax, in which case you better be able to back up your rulership.
If you want an empire spanning multiple regions, each extra region must have a vassal as its local ruler. You can decide whether your vassals get to set their own taxes, how much of the taxes they must pay to you, and so on.
Anyone who ends their turn in a region with a savagery value higher than 0 risks being attacked by a monster. The value is tested by the GM with 1d100, if the roll is equal to or lower than the value a monster will attack. The roll is increased by 5 for every character beyond the first in a region. If there are any empty monster lairs in the regions then a new monster will appear, otherwise a monster from one of the lairs will attack. If the monster survives the fight, it will return to its lair/claim an empty lair.
Whenever a monster is killed, the region's savagery will decrease by 10.
(There should be different types of monsters: some that try to kill you, some that steal your stuff, some that eat your food, and so on.)
Each magic spell is its own skill, and consists of a verb and a noun. These can be chosen freely by the player, and decide the effect of the spell, though the GM might specify it further. Casting a spell requires a number of ingredients, chosen by the GM (Destroy World would be a very expensive spell).
You can cast three spells per day without paying any actions, and any spell you cast after that will cost one action.