that'd be around the 3rd movie if they follow the story.. I just play the games but I did raid and before WoW came out I played the shyt outta warcraft 3 and had warcraft 2 as well
from the trailers looks like its following the story and this movie will be about Orcs leaving Dreanor and coming to Azeroth where the humans are(Warcraft 1 and 2), the next movie or the end of this movie will probably introduce undead, night elf, trolls and tauren(Warcraft 3) and then they join together to fight the plague but still hate each other(Warcraft 3 -> World of Warcraft). Everyone in this movie should be pretty much irrelevant by the 2nd movie where it'll be more based on Thrall, Jaina, Arthas and Illidan (if they follow the story line) and the 3rd movie should be the end of Arthas/Lich King (wotlk)
everything after wotlk is pretty much just filler and probably wouldnt fit in a story anyway (especially worlds of dreanor)
I doubt they go into the sunwell story or shyt like that.. probably only the main areas (Dreanor, Azeroth, Black Temple and Ice Crown)
Blizzard fukked off the Illidan story line so much in the original Burning Crusade im not even sure if they'll even go or talk about the Black Temple but im pretty sure it all leads to WOTLK/Ice Crown/Lich King in this movie series
edit: im just speculating of course, but the first movie is definitely based off Warcraft 1+2. This damn video game series so damn long they might not even do the Lich King arch.. they might just go to Naxxaramas but people would probably just call it a lords of the ring clone if they did that way