Yeah, Stevenson does a great job of layering the perceptions sight, sound and physical description David has of Ebenezer. It seems the most natural thing to have occur: David approaches from afar so first he perceives visual clues to Ebenezer's identity. When he arrives at the door, he then hears sounds. Finally Ebenezer presents himself and his person reveals more. Though it seems merely natural progression, it fits Stevenson's literary theory that the right thing at the right time and in the right place creates indelible images in readers' minds, images that live for years after reading a work.
All three isn't it?! I think certainly the fact that he is carrying a blunderbuss doesn't do much to convey a sympathetic image to either David or the reader. In addition, of course we need to mention the sparse gothic setting of the House of Shaws, which we are told is partially unfinished and somewhat ruinous. These facts, combined with the miserly habits of Uncle Ebenezer, certainly foreshadow dark events to come...
I would have to definitely say that at least the description of Uncle Ebeneezer is not that flattering and his description is somewhat creepy to foreshadow crazy things that will happen later on in the story. It should be very clear after his initial description.