All English Bibles are translations, sometimes translations of translations. There is more than one way to translate various words or phrases, differences in say, the LXX as opposed to the Masoretic text, and differences between the old Vulgate as opposed to the Clementine Vulgate. This isn't necessarily a bad thing.
The Knox and the Douay are just different versions of the same scriptures, some prefer the former, some prefer the latter. Personally I prefer the Knox version, but that's just my preference. If you like the Douay Challoner version than use it. It's hallowed by Catholic Tradition in the English speaking world and, correct me if I'm wrong, still considered acceptable to use even by modern churchman. I think if I recall correctly the USCCB used to have something on their website about how the Douay is still perfectly acceptable.
Catholic Answers serves a purpose I suppose, but it certainly can become a hothouse atmosphere of recent converts and those addicted to winning arguments or having ready answers for every question. At some point it's best to step away from that sometimes toxic scene.
I would agree on points two and three here. Whichever version that you prefer to use is fine, both are good bibles and both will give you a good understanding of the Scriptures, so don't worry about what Joe Shmo tells ya. I personally use the Douay-Rheims (but I like Knox a lot). I don't know why, but if I ain't hearing "thou, thee, thy, thine" or "Shew unto us, O Lord" I really just can't take it serious.
And FB is right about the Catholic Answers, or really any online discussion site (yes this includes Fisheaters, sorry!). When I converted it really tickled my pride thinking I had all the answers to everyone's questions (and I still do, become Catholic, "and do everything he tells you"
), but, from personal experience, I would recommend avoiding controversial discussions or debates. They can get really nasty, especially with protestants, atheists, and particularly apostates. We should always get our spiritual lives in order before we go into arguing and debating. (I am not saying that there is anything wrong with studying apologetics nor discussion and healthy debate, not at all, it can be a very good thing, but the temptation to get argumentative and proud is always there, and an easy ditch to fall into. ) Anyway, that is just my two cents.