if i go above maximum bandwidth usage, which error page will be displayed? which page number? 404, 530 or one of those.

"Suspended" page

400 (Bad request)
401 (Authorization required)
403 (Forbidden)
404 (Wrong page)
500 (Internal server error)

"suspended" is not on the list!

that is the list on cpanelX

Suspended page does not have an own error code. When your account is suspended you index page is replaced with cpanel suspended page and returns 200 code

yes, i know, i only want to say that if you overuse your bandwidth your account will be suspended if you don't contact the support staff (i have read it in some forum post)

Exceeding max bandwidth don't give you an error page.

still a bit puzzled.
does the suspended page list my email address (so visitors can contact me) or will all mail traffic be suspended as well?

Suspended account has no traffic.
Also suspend page does not contain email addresses of customer.

Any visitor can whois your domain and email you.