The realization of highly efficient, highly coherent, and scalable sources of single photons that can be integrated with on-chip optical networks is of great interest for creating photonic quantum processors. Here, we successfully implemented efficient spot-size converters in planar nanostructures using a novel fabrication method that integrates optical polymers with suspended waveguides. By further integration with a quantum-dot-based single-photon source on III-V semiconductor platform, we realized a quantum optical interface for lensed fibers, resulting in 48% chip-to-fiber coupling. Additionally, we demonstrate a novel resonant excitation scheme that leverages the potential of planar nanostructures. Through careful on-chip optical mode engineering, we achieve >80% single-photon coupling efficiency into the waveguide, while maintaining laser suppression better than <10-4. The resulting on-chip single-photon source exhibits high-purity (g(2)(0) = 0.020 ± 0.005) and high-indistinguishability (V = 96±2%). To demonstrate the potential of the integration and scalability of the platform, as well as packaging, we provide preliminary results of multiport coupling for chip-to-fiber-array as well as chip-to-chip interfacing. These collected investigations explore a pathway towards a complete plug-and-play single-photon source where multiple QDs can be triggered simultaneously to emit coherent single photons with high purity and indistinguishability.