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Cold spray additive manufacturing (CSAM) is a solid-state deposition process that largely preserves feedstock microstructural features in the bulk deposit, making tuning of powder properties a direct lever for engineering deposit performance. This characteristic is particularly attractive for the fabrication of components subjected to extreme, directionally biased thermomechanical environments, such as the walls of rotating detonation engines (RDEs), where GRCop-42 (Cu-4Cr-2Nb at.%) is a leading candidate material. Realizing feedstock-driven microstructural design in CSAM requires upstream control of the powder itself. Ultrasonic atomization (UA) offers systematic control over droplet solidification conditions, and therefore over powder microstructure, prior to deposition. In this work, 17-4 precipitation-hardening (PH) stainless steel is used as a model system to establish process-structure linkages across the UA parameter space. A two-factor full-factorial study varied torch current and gas recirculation rate, and the resulting powders were characterized by particle size distribution (PSD) analysis, scanning electron microscopy (SEM), backscattered-electron imaging, inert gas fusion, and instrumented microhardness. A single-particle micropillar compression test within a SEM was also performed. The results demonstrate that UA processing parameters systematically influence powder impurities concentration and internal porosity, with dissolved oxygen and nitrogen content tracking together in a manner consistent with a cavitation-driven gas-entrainment mechanism. Single-particle testing further revealed ductile deformation without fracture, indicating feedstock deformability relevant to cold spray consolidation. Together, these findings lay the groundwork for feedstock-informed materials design in CSAM.