I'm not sure about the spam emails, I don't get them but there is likely an opt-out/unsubscribe link at the bottom of the email.
You also need to understand that they don't allow streaming, tethering, or downloading files/apps via cellular data. (Granted you can since theres no technical limitation, its just ToS verbage). So just browsing the web or checking email is not likely going to get you in any trouble. The limit is 100MB btw, we just tell people this on Hofo since its a safe conservative limit. I have done 300MB in a day before without getting any warnings or data cut off. Its not that strict or laid in stone like what you've described.
ST isn't for everyone. If your getting ST, I do certainly hope you understand the limitations and are ok with it. For those that do find it a good fit, its definitely a very very good value.