1) By default, the email notification is sent when the ad actually expires (as this is triggered when the ad itself expires and goes back to draft mode), but membership/subscription expiry reminders are sent prior to actual expiry.
2) The current ad pack options do not have additional options for the number of images.
3) You can set a price per category option, as well as allowing certain categories to be posted in only if a membership/subscription is purchased.
Any changes to the default functionality would require customization on your part. ClassiPress is not encrytped, so you are free to make modifications if you wish. AppThemes does not offer customization services, however we do have a
certified partners page where you can find developers for hire. If you make contact directly with an outline of your requirements, they can provide a quote for the work. Thanks :)