Abstract: Galaxies don’t reside in isolation. Their outskirts contain a hidden ecosystem of faint stars and stellar systems that trace the history of their hierarchical growth through mergers --- one of the most important drivers of galaxy evolution. This dissertation aims to uncover this historical record and constrain the processes that govern galaxy formation and evolution across a wide range of mass scales, from Milky Way (MW)–like systems to their ultra-faint dwarf companions. Although mergers can strongly influence the diversity of structural properties seen in galaxies, the resulting dynamical response often erases the observational markers needed to infer the characteristics of the merger. However, simulations show that material accreted into a galaxy is retained by its stellar halo, preserving a "fossil record" that we can trace with resolved-star observations. I present the deepest stellar halo map of the nearby galaxy M94, revealing that it has one of the smallest and most metal-poor stellar halos among MW-mass galaxies (M*=2.8x10^10 M☉, [M/H] ~-1.4) and indicating that its dominant merger was with a galaxy less massive than the Small Magellanic Cloud (SMC). M94 also hosts the largest pseudobulge in the Local Universe, but this work suggests that it was shaped primarily by secular processes rather than by this dominant merger. I also illuminate the structural diversity of faint satellite galaxies around M81, finding among them the most compact (DWJ0954+6821), most concentrated (D1006+69, n ~ 5), and one of the most elliptical (D1009+68, ϵ ~ 0.57) dwarfs known in the Local Volume. This work improves on ground-based characterizations of these systems and reveals that all four satellites are metal-poor and quenched, with no evidence for tidal stripping despite their varied ellipticities. Lastly, I successfully demonstrate the feasibility of wide-field, multi-object fiber-fed spectroscopy in a low signal-to-noise regime for probing halo kinematics beyond the Local Group, presenting the first measurement of the line-of-sight (LOS) velocity and velocity dispersion of NGC 253's stellar halo. I find that the stellar halo exhibits prograde angular momentum and detect kinematic substructure coincident with its known southwestern shell, consistent with a recent accretion event. This work lays the foundation for conducting resolved stellar population science with next-generation observing facilities such as the Rubin Observatory, Roman Space Telescope, and the Extremely Large Telescope.