What email do you use for adsense? Personal, Complete Separate, or the same one you use for your website? I read that you can not change the email once it is setup, so I don't want to make the mistake of putting in a bad email
You can use whatever email you like. You read wrong. You can easily change your email address as per Adsense's instructions: https://support.google.com/adsense/answer/161758?hl=en
AFAIK, Adsense will always ask for your associated Gmail account so it's pointless avoid using Gmail to signup. I signed up using my own domain email address and shortly after was required to switch to a Gmail account as main login, but still can add other associated accounts. Therefore my advice is using your Gmail account but not your personal one. Make a new Gmail account for the sole use of Adsense and any other business you make online. This will contribute to keep all your business moves into one place.