In this work we outline our multiscale approach for modeling electronic, optical and transport properties of III-N-based heterostructures and light emitting diodes (LEDs). We discuss our framework for connecting atomistic tight-binding theory and continuum-based calculations and how finite element and finite volume meshes are generated for this purpose. Utilizing this framework we present an initial comparison of the electronic structure of an (In,Ga)N quantum well carried out within tight-binding theory and a single band effective mass approximation. We show that for virtual crystal approximation studies, a very good agreement between tight-binding and effectivemass model results is achieved. However, for random alloy fluctuations noticeable deviations in the electronic ground and excited states are found when comparing the two methods. In addition to these electronic structure calculations, we present first LED device calculations, using a drift-diffusion model.