No a factory reset won't do that. You will have to format the SD Card partition of your phone, which will delete all your pics/downloads/some app data etc.
Correct, our GNex will not receive the official 4.4 because TI dropped out of the mobile game so we wouldn't get updated drivers, but some were found hidden in our system I believe so the ROM devs will be able to put these to use!
If it won't even turn on I doubt it was the OTA that broke your phone...sounds like your battery is dead and isn't charging either. Where was battery % at when you turned it on and did you have it charging while it was doing the update?
Re: emerging into the world of flash and ROMs. a little confused.
ROMs aren't "super apps" its custom Android firmware/OS that devs merge the code together from the AOSP. You can download ROMs from apps like ROM Manager or GOO Manager or you can just download them straight from the devs...
If your using Windows make sure you put your recovery.img in the same directory as ADB:
cd to the adb/fastboot directory ie. cd C:\ADB
adb reboot bootloader
fastboot flash recovery recovery.img
If your using Linux/Unix:
cd to where your recovery.img is ie. cd /home/username/Desktop
adb reboot...