Web App GUI design for Music Sequencer

We require the design / build of a user interface for a music sequencer web app. The app can be seen at [login to view URL] The current interface is purely to allow testing of its functionality. It now requires the designed/graphical build. I have attached a photoshop mockup of the type of look/feel that we seek. We will require you to establish and maintain communication with the developer who built the app in order that the design can be implemented in precisely the way it was intended. A musical background or understanding is considered important as well as familiarity with how sequencers/DAW's work. We will need suggestions on design choices that make sense practically and not purely design choices that look good visually. The aim is to of course achieve both. Project files will need to be organised and ready for revisions to be made should either the app developer or M:Tech request them. This would be expected in a timely manner.