You can't play dota without installing warcraft 3.
There is no world of warcraft 3. There is world of warcraft, and warcraft 3. Unless you want to refer to Cataclysm. If so then no, you'd fail.
Warcraft 2's expansion, Both Warcraft 3's and World of Warcraft are all online play. warcraft 2 and 3 use battle.net, while World of Warcraft is a paid subscription MMORPG
Sadly, you can't
Not without outlandish modifications - World of Warcraft is a game for PC and Mac.
about 4 million
You cannot be him but you can battle him in the Undead campaign.
You do not have to pay to play the game, you just have to pay for the disc.
This is a very broad question, much like saying "what is a human". Depending on the map, who created it and what it was intended for, there can be infinite answers to this, but looking at it as a strategy game (Warcraft 3 Default Maps and Units), you may train units at the various buildings in Warcraft 3. Sources: I play Warcraft 3 a LOT. :)