We studied the clustering properties and multiwavelength spectral energy distributions of a complete sample of 162 Ly alpha -emitting (LAE) galaxies at z unk 3.1 discovered in deep narrowband MUSYC imaging of the Extended Chandra Deep Field-South. LAEs were selected to have observed frame equivalent widths >80 AAA and emission line fluxes >1.5 x 10 super(-17) ergs cm super(-2) s super(-1). Only 1% of our LAE sample appears to host AGNs. The LAEs exhibit a moderate spatial correlation length of unk = unk Mpc, corresponding to a bias factor b = unk, which implies median dark matter halo masses of log sub(10)M unk = unk M unk. Comparing the number density of LAEs, 1.5 plus or minus 0.3 x 10 super(-3) Mpc super(-3), with the number density of these halos finds a mean halo occupation similar to 1%-10%. The evolution of galaxy bias with redshift implies that most z = 3.1 LAEs evolve into present-day galaxies with unk, whereas other z > 3 galaxy populations typically evolve into more massive galaxies. Halo merger trees show that z = 0 descendants occupy halos with a wide range of masses, with a median descendant mass close to that of unk. Only 30% of LAEs have sufficient stellar mass (> similar to 3 x unk M unk) to yield detections in deep Spitzer IRAC imaging. A two-population SED fit to the stacked UBVRIzJK+3.6, 4.5, 5.6, 8.0 mu m fluxes of the IRAC-undetected objects finds that the typical LAE has low stellar mass ( unk x unk M unk), moderate star formation rate (2 plus or minus 1 M unk yr super(-1)), a young component age of unk Myr, and little dust (Av < 0.2). The best-fit model has 20% of the mass in the young stellar component, but models without evolved stars are also allowed.