We don't have a "change zip code" link, but we could add one in the next update (good suggestion).
We dont have a subscription program like that - the ads are a pay as you go format at this time; but we will be adding usergroup discounts for prices in a future update.
You can set up to 6 extra fields per category; adding more would require doing just what you outlined (and adding a little php code to insert the new fields).
There is not a "tell a friend", but we have slated for the next update a "send via email" so that ads can be sent to anyone via email.
Ads expire at the end of the term selected during placement of the ad - warnings are sent to the user offering to allow them to be extended if needed. There is no "no expire" option, but it could easily be added by changing the template.
Ads don't delete (unless explictly deleted) when expired, they go into an "inactive" state where users can still see them or renew them via their My Ads section. Images are removed when ads are deleted.
Please do not PM me for support or sales questions. Thank you for your understanding.