I successfully rooted by following these 3 guides/links to help me root and still be on 12b:
http://androidforums.com/metropcs-o...rooting-f6-recovery-updated-12b-4-9-14-a.html (to root) follow this guide AFTER downgrading your phone to 10i via link below (2nd link). (sorry for guide being out of order). You have to follow guide/link below first.
Unbrick/Unroot/Factory Restore - Android Creations (downgrade to 10i in order to attempt root via first link above)
Root and 2nd-init CWM Recovery - Android Creations (minus the cwm), used it as a guide to backup the root so that when I upgraded to 12b, I can get the root back by saving the root, since 12b cannot be rooted without rooting on previous firmware). This is to bring the root over to the latest firmware.
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For the storage thing:
This guide for external/internal storage swap:
http://androidforums.com/lg-optimus-f3/801368-mod-app2external_sd-fixed-duplicate-files.html. When in SManager, make sure you long press the "11extsd2internalsd.txt", press script/execute, and check the su, boot, and save. You'll know what I mean while following this guide. I believe this method is to allow the phone be able to download/install high gb apps to an extent.
And this guide as the last:
[Guide] partition and link2sd [pictures included for each step] - xda-developers. This is so that after installing a high gb app, it'll then link/move directly over to the SD card via Link2SD, since the above solution only allows the phone to temporarily download a certain amount of high gb apps. After the the apps go to the SD card via Link2SD, you will be able to download/install more without the "insufficient storage error" coming back I assume, since the apps moved over to the actual partition. NOTE..If you have a big SD card like 14gb or higher, feel free to make your "EXT2/3/4" bigger, because the guide tells you to set it very low like "512mb" which is obviously not enough.