5. Make really,
REALLY sure that no important thing is still set to the old address.
At $Work, we received a domain registrar password reset e-mail today - for a former client who I don't think we've talked to in 15+ years. Banks, registrars, etc. seem to store stuff like e-mail addresses in more different fields, in more different databases, than any 3+ of their customer service rep's can find & fix right.