In answer to your questions:
1) The default number of images is 5, but there are no specific image size limit settings within the Vantage admin dashboard. It would require customization on your part if you were looking to add these restrictions.
2) There is no option for membership pricing at this time, so this is not available by default.
3) When you set up pricing plans, you determine the duration for which the listing is displayed. When the listing expires, the user is emailed to advise this and that they can renew. The listing itself is sent back to draft mode once it's expired, thus is not published.
Vantage is not encrypted, so you are free to customize it to suit your needs. If you are looking for developers for hire, we have a
certified partners page, where if you make contact directly with an outline of your requirements, they can provide a quote for the work. Thanks.