Three mysteries in Wuthering Heights

Three mysteries in Emily Bronte's "Wuthering Heights": first, where did Heathclifff really come from? The highly dubious account from Mr. Earnshaw just doesn't stand up to reason - that he was going to Liverpool (sixty miles away) on business for 3 days, walking the whole way, and he promises to bring back gifts for his two children, Hindley and Catherine, and he comes back with this dark, "gypsy-like" waif under his coat and more or less forgot the 2 promised gifts. Does it make any sense that he saw this urchin on the street, took pity on him, and brought him home? Of course not - the only likely explanation is that Heathcliff is his out-of-wedlock son, whom he's claiming to raise. The arrival of Heathcliff may explain the early death of Mrs. Earnshaw. The odd provenance of Heathcliff may explain why he has one name only: Earnshaw won't claim him as one of the family (an Earnshaw) but won't deny him (with another last name) either. Also may explain the dangerous attraction between Heathcliff and Catherine, and the morbid jealousy of Hindley. My guess is that Earnshaw never even went to Liverpool - that he claimed Heathcliff in some nearby village (he could not have carried him for 60 miles). Second: where did Heathcliff go for his three years of absence, when he matured into a handsome and dangerous and love-sick man? There's speculation that he went into the Army, but that seems unlikely to me - he has no military presence whatsoever. He seems to have made a fortune somehow, and it appears that he returns to WH to claim Catherine, only to learn that she has married Linton. Where did he go and why was he completely out of touch - or was he? Was he in London, America, in prison? He never says - perhaps he was trying to learn the answer to the first mystery, that is, trying to figure out who he is and where he came from. Third: what happens while Ellen/Nelly is held prisoner in WH, captured during her visit to WH with Cathy, and held by Heathcliff in an attempt to engineer a marriage between Cathy and the mortally ill mil-toast, Linton. Perhaps Bronte will answer this mystery by the end of the novel - but it seems extremely odd and tantalizing that she builds this hiatus - the gap in the transcript - right near the climax of her story. What happened that Ellen could not see and cannot narrate?