I don't disagree that elements of Christianity are present in Tolkien's mythos, the allegorical representation of Eru as God and Morgoth as Lucifer are glaringly obvious, as is the death and resurrection of Gandalf. However, Tolkien makes no indication that the final destiny of men is to live in the presence of Eru or Morgoth. He is however, very specific regarding the fact that men are not tied to the destiny of Arda and are released from it upon death. That is all we know. It seems presumptuous to conjecture one's opinion as fact when the OP has asked for the "facts" regarding Tolkien's mythos. Additionally, Tolkien drew from Norse mythology as much as Christianity to write his epic, with that in mind, attempting to match 1:1 the elements of Tolkien's mythos to Catholicism (Halls of Mandos:Purgatory) completely ignores the fact that many other epics he read influenced his writing.
I'm not saying that there is no parallel between the Halls and Purgatory, or the LOTR afterlife and the Christian afterlife, only that the symbolism (intentional or accident) go beyond Catholicism.
In regards to the hobbit afterlife, according to the one ring wiki (such a scientific reference, right;) ) Hobbits are a subset of men thus are entitled to gift of men as well.
I can't speak for orcs. On the one hand, they were created from elves who were corrupted, which would lead me to conjecture that they inherit the gift of the first born. However, we know that isn't true because there is no mention of the orcs wandering around in the halls of Mandos. On the other hand, as they have fallen from grace (a common and powerful theme in LOTR) they receive no gift and cease to exist upon death. Having said that, I will add, this is only my opinion formulated on my understanding of the Tolkien mythos and I have nothing to support that claim.
As a final note, Draugluin, I am engaging in a friendly debate and do not wish to offend, regardless of our interpretation of the LOTR afterlife, I will not flame or call you names
. If my language comes across as strong, it is unintentional (even if that means we have to agree to disagree).