Greetings, Sean! Thanks for reaching out to the Apple Support Communities! It sounds like you are having issues reinstalling OS X on your computer and I am more than happy to help! You have tried some really good steps so far and at this point, check out this article with alternate steps to follow for How to reinstall macOS. For your second question about creating an external installer, I would check out this article with steps for How to create a bootable installer for macOS. Cheers!
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