I don't own one of these rigs, but I have a lot of experience doing mods to the 703N. There isn't an SD card if it's a stock device, but there are probably ways to get a copy of the firmware if you want to play around with it (of course, you might break it too, so be careful). Lots of info here:
http://wiki.openwrt.org/toh/tp-link/tl-wr703nPost the hash file of the root password, I wouldn't think it'd be too hard to decrypt.
I can't ssh the controller, so I can't extract the file. Maybe there is an SDCard inside the controller. Didn't think about that. Will check.
No, ssh doesn't work, but it seems to respond to FTP and SCP, haven't been able to break the password though