MacBook Pro mid-2012 have to wait 30min between reboots
Some Mid-2012 MBPs had an issue with the Hard Drive Flex cable that could cause similar issues (at least as far as the Booting to a Folder with a Question Mark), so I might be worth calling Apple or heading to an Apple Store to have them have a look.

If it is one of those ones, you may get a repair for free for it. I gotta stress though, it isn't ALL mid-2012s, just some of them. Mine wasn't one of them (I had permanent "No Hard Drive Detected" but the tech I saw initially thought it was, hence me knowing anything at all about it).

If it is the cable that is faulty, it didn't cost a lot out of warranty anyway, although if you are getting the odd Prohibitory symbol, then you may want to reformat the drive and reinstall OS X anyway to get rid of any filesystem problems that would still be there beyond hardware