I know some people on here will be able to help you with the public transportation thing, but just as a warning...IT'S NOT GOOD! I'm sorry, but the vast majority of the US is terrible when it comes to public transportation and ALL of the US is terrible in public transportation outside of major cities. Good luck with that.
As for the FlashPass, see what crowds look like and if they are bad or you want multiple rides on the big coasters then absolutely go for the Gold Flash Pass. I would never really go for Platinum, but I also wouldn't go for the entry level one.