APEX/Visual App integration with external REST API

Looking for an experienced Salesforce developer to help build a apex/visual application that integrates with an external REST API to WebMerge (www.webmerge.me). The main purpose of the app will allow a user to link WebMerge documents to SF Objects and send data to be merged into those documents via a click of a button. Our internal development team will assist in any API needs/development and will work alongside the SF developer. Top Level App Functionality Requirements: - Allows a user to pull in a list of their WebMerge documents - Allows a user to "map" SF Object fields to the fields in a selected WebMerge document - Automatically adds a button to that SF Object page for each "click to merge" functionality - Save merged documents as an attachment to the SF Object Other Requirements - App testing must be built to meet 75% code-coverage requirement - App must be built to pass SF review and guidelines