Custom Outlook Add-in Development

I am looking to sign up to a cloud-based CRM system called SalesSeek. This has an open API details can be found here; https://salesseekapi.atlassian.net/wiki/spaces/SA1/overview
My team of salespeople works a lot in Microsoft outlook and I want a way to import emails sent and received into the SalesSeek CRM system. I need a simple outlook addin to work in the desktop outlook application that will provide a button for the user to click that will search SalesSeek for the email address of the selected email and if it finds it then link the email into the CRM against the correct contact. If we were to go ahead I would want to start immediately.