By phylogenetic inference, since the machinery for DNA replication is not universally conserved (is different in bacteria vs archaea, often taken to imply that the DNA replication machineries in both domains evolved after the split of the bacterial and archaeal lineages from the last universal common ancestor), and since de novo DNA biosynthesis are elaborations on the pathways for de novo RNA biosynthesis (basically, that cells that synthesize the monomers of DNA first synthesize the monomers of RNA and then further modify them), yes, in fact there is evidence that implies that RNA preceded DNA in evolution.
No, not entirely like a modern translation system. But why would it have to? There is some evidence that the core RNA component of the ribosome can actually catalyze peptide bond formation in the complete absence of protein.