Update and add database to exsisting site

I have a property rental website that currently has no database. I am looking to extend the site with the help of a database and also allow customers to pay online. I would like to have the facility that people can upload their own details onto the site as used by other sites such as [login to view URL] I am also keen to keep a similar image to my site [login to view URL] and maintain a the high search engine position I have worked for over the years!