A unified analysis is presented of submonolayer nucleation and growth of two-dimensional islands and the subsequent transition to multilayer growth during metal-on-unreconstructed metal(100) homoepitaxy. First, we review and augment recent developments in submonolayer nucleation theory for general critical size i (above which islands are effectively stable against dissociation). We discuss choices of "capture numbers" for aggregation of adatoms with islands, and ramifications for island density scaling with deposition flux and substrate temperature. We also characterize a "direct" transition from critical size i = 1 to a well-defined regime of i = 3 scaling, with increasing temperature, for sufficiently strong adatom-adatom bonding. Pie note that there exists no well-defined regime of integer i >3. The submonolayer island distribution provides a template for subsequent unstable multilayer growth or "mounding" (which we contrast with "self-affine" growth). This mounding is induced by the presence of a step-edge barrier for downward diffusive transport in these systems. We characterize resulting oscillatory height correlation functions and non-Gaussian height and height-difference distributions. We also develop an appropriate kinematic diffraction theory to elucidate the oscillatory decay of Bragg intensities and the evolution from split to nonsplit diffraction profiles. Finally, we analyze experimental data for Fe(100) and Cu(100) homoepitaxy and extract key activation barriers for these systems.