OK, about raids being changed to "public" zone, I am not entirely sure how to do that. It is definitely possible, I just don't have time to figure it out right now.
About guilds, in worldserver config file are settings for two-side interractions between factions. You can set that Horde and Alliance players can chat, party, guild and so on with each other.
About guild wars, if you mean something like battle between 2 guilds in some sort of battleground, I have only one idea how to do something like that - you may set that zone as free for all PvP area (FFA PVP, like Gurubashi arena is), and players would battle there in raid vs raid battle. Real guild vs guild battle probably is not possible at all.