There really isn't a great Septuagint version in English, so you can take a look at all of them, but it won't really matter which you pick in the end. If you Google septuagint translation (or something like that) you should pull up some pages that have multiple attempts at a translation. As far as the RC Bibles, as far as I know, they don't follow the Septuagint's readings (in the non-deuterocanonical books), but only take the names and book order from the Septuagint (rather than the Hebrew version), and accept (most of) the extra books in the Septuagint. RC Bibles are sort of like a half-Septuagint, half-Hebrew translation.
Jerome was very much against using the Septuagint, and thought that the Hebrew was superior, so he generally translated from Hebrew rather than Greek. The only reason Jerome translated any of the deuterocanonical books at all is because, according to tradition, he was pressured into doing it so as to placate a clerical friend of his (if I remember correctly). He bragged that he had translated one book in a single sitting (it was Tobit I think--my favorite O.T. book, not that it matters). It was only after Jerome's death that other people appended the other deuterocanonical books to Jerome's Latin Vulgate. This wasn't especially important, since Jerome's version took a while to catch on anyway; people in the west at the time much preferred the older Latin version.