I count on 2-5 years of development.
the worst thing to make a mistake with the architecture of the beginning.
and the need to do a lot of tools that will help simplify and speed up the work: how wysavig - for ordinary people.
1) Monsters: parameters, drop sets, range of attack, time and place of occurrence. attack range, the model animation.
2) from the drop sets, and there are things drop rate (uslviya quests).
3) things have: the model, requirements, modifiers
4) quests - scripts: the ability to use the monsters, players, grid, chain quests. NPC dialogues. game events.
5) global gaming events: the siege, opening event
6) chat: clan, group, raid
7) Grid: a graph on which you can set objects (map editor), calculation of distances between objects, used in AI and NPC monsters
8) Map Editor: ability to set the scenery, set the monsters, set the NPC.
Editor: quests - the opportunity to write the script and bind to each other all that is in the game
9) Editor of things: the creation of descriptions of things. creating drop sets.
10) the table of characters experience
11) skill Editor
All this should quickly communicate without errors