Am I correct in that when determining the maximum limit of flood insurance coverage for a farm loan that contains dwellings, barns, outbuildings, etc., that the residential dwellings would each have a max. limit of $250,000 coverage and each of the barns/outbuildings (assuming they are insurable) would have a max. limit of $500,000 coverage?

Yes. As for as the NFIP is concerned there are "residential" and "non-residential" structures, so a barn would be a non-residential structure (unless you counted the livestock).