I, too, have a very limited internet 'gigage' each month (8 gig wireless broadband is all we can get in the sticks).
Was a good girl and uninstalled all my WoW files, double checked the system to make sure nothing was skulking around, did a system clean up, added my game key to my account, then put in disc 1...
...which took an hour to install 0.3%...then it asked for disc 2.
I put that in and it took another half an hour to get to 0.4% install...and it's been sitting there ever since (another 20 minutes).
I'm on a pc, Win XP & Chrome.
*Edit: never mind. Just read OP's update, and as mine has just hit 5% and the process has been the same as his, I'm assuming all will go well at 6%.