Is there any way to reach say.. 1 - 2GB total? I know realistically i can't delete any DBC files obviously, but i can empty it's rows right? Anything else that needs to absolutely stay in the client or itll explode?
Yes. There are only little entries really needed, like those in Startup_strings and videohardware. Most other dbcs can just be emptied without loss of anything.
Is "common, common-2" etc all looked for on startup.. could i leave them in with zero content, or 1 row of content..?
Just let them be empty except for that one MPQ you need. Or even try removing them. Some of them are not required.
In the end, just first extract _everything_, to have the latest version of all files. Then, move all MPQs away and start the client. It will tell you if it is missing something. Then, add empty MPQs for those it is missing. Then, add the files it complains about missing to one of those MPQs (common.MPQ, locale-****.MPQ, likely). Continue until you are at the login screen. From there, you can go the other direction again: remove stuff from gluexml you don't need, i.e. models, textures, buttons, Then, enter world. Repeat.
In the end, some pretty low level dbcs should be required to get to login. Pretty much everything than event handling and calls to enterworld/defaultserverlogin and character selection should be left pre-enterworld. enter world will require map.dbc, a wdt, light.dbc and some other basics, but they can be empty except for one entry each, most likely.
tl;dr: remove everything, add what it complains about.
