The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul). The guides have been tweaked many times over the years to make things "faster". The leveling guides were made because of all the messages I got from people asking me how I was able to level up so quickly on new realms. I was first to level 60 on 7 different realms (3 with Mancow and 4 with Joana), even winning Blizzard's "First to Level 50" contest they held back in 2006.
Even though a modern server architecture is used, Classic servers won't have the same features that current World of Warcraft does. There won't be cross-realm servers or Looking For Raid and Dungeon Finder automatic party matchmaking. There are still a lot of questions about how the team will tackle it. This endeavor is being undertaken by an entirely separate team at Blizzard from the one working on World of Warcraft and its next expansion.
Players will start from level 1 and will progress through level 60 with real, Blizzlike x1 rates. Old PvP battlegrounds are: Warsong Gulch, Arathi Basin and the famous 40vs40 players Alterac Valley where battles were known to last more than 24 hours. 20 and 40 man raids will be available for Molten Core, Zul Gurub, Blackwing Lair, Ahn'Qiraj 20 & 40 and the original Naxxramas raid in the Eastern Plaguelands.