develop a system on my website to be able to automatically send emails for when a service is due

We have a pest control business I was after someone to develop a system on my website to be able to automatically send emails for when a service is due. Below are some examples: We inspect houses for when people buy a house and after 12 Months would like an email sent out automatically after 12 Months offering another inspection. We Do a Termite Treatment and after 12 months people need another inspection to maintain the warranty period (5 to 8 Years) and would like an email sent out automatically after 12 Months offering another inspection. We do General Pest Control and would like an email sent out automatically after 3, 4, 6 or 12 Months offering another another service. We do pest control services to shops, cafes, restaurants, warehouses etc…. and would like an email sent out automatically after 1, 2, 3, 6 or 12 Months saying that their next service is due. I currently use the wordpress theme canvas and use Gravity forms and need to work with this, I really don't want anyone on the back end of my site changing settings that I don't understand. Please give me an example of how you would achieve this. Our website is: [login to view URL]