Balance and testing will determine the final number. However, Blizzard will not promise any of these until they have tested the idea to see if it's actually fun and entertaining. A questing game type is an interesting new addition that can be played cooperatively or competitively. The quests will most likely be ones with relatively simple objectives such as killing a specific hero, destroying a certain building, or searching a specified area. Upon completion of these quests players might be rewarded with magical items, gold, a new unit, or other such things.
All races are playable in multiplayer and are balanced so that each has an equal chance of winning.
In addition there are hostile neutral units which provide even more possibilities for multiplayer games. Races are being designed to complement each other in battle, so that a team of two different races will have unique abilities that the two individual races would not have on their own. It is not known for sure exactly what this means, but a possible special interaction is that different heroes of different players on the same team confer special benefits to each other. Hopefully this will increase cooperation and strategy. WarCraft III will offer new advantages and incentives for alliances.