Look for the pre rooted Odin tar - it will give you root and a custom recovery in one step, and is currently one of the easiest root methods available.
As for the file renaming, using the Odin method will bypass any need for it - as long as you make sure "auto reboot" is NOT checked, you can safely disconnect the phone when the Odin flash completes, remove and replace the battery (I might have that detail mixed up from my OG Epic days, but the correct instructions will be found with the Odin file), then boot into custom recovery before
anything else, you can flash your custom rom and reboot as normal.
Since you'll be flashing over a mostly factory-fresh stock rom (root is the only change), you shouldn't need to do the factory reset (I think some recoveries for our phone do correctly preserve the internal storage, but I can't remember which ones). And the part of the stock rom that replaces the recovery with stock will only run when the rom (not recovery) boots, so by flashing a custom rom without ever booting the stock one, you bypass that issue completely - that's why you don't want Odin to auto reboot your phone after the flash.
I think I've covered the important parts to get you up and running, but I'll double check your post for any questions that I missed. If you end up with more questions, don't hesitate to ask
Edit: I did miss some things
Can I go back to stock recovery?
- sure, but there is no good reason to unless you're returning to complete stock in order to sell the phone or to have it repaired or replaced... the easiest way for that is to Odin the non-rooted stock tar package
How do I flash a ROM using the internal memory?
- it should work, I did this yesterday using CWM Touch. The possibly confusing part is that the internal memory is considered an sd card, but if you see two options then one will be clearly labeled as external (I say if because I don't know whether any recoveries hide that one when no sd card is actually present).
How do I do this with adb (assuming I have to).
I actually don't know the answer to this one, but if you use the Odin method then it won't be necessary
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