How to Create Template Merge Fields for SQL Server Connections

I am working on a project for a contract management system. The data resides on a SQL Server backend. I need to create Docusign Templates for many state-specific and generic contract documents. I am familiar with Salesforce merge fields, but I need the same capability for this project. I understand I may need to build a custom connector in order to connect to SQL Server databases. I need help or guidance on how to go about this.