Eloise and Charles seem to still be in contact, therefore Eloise could have given Charles access to the Lamp Post.
Charles Widmore had someone at the arctic/antarctic station inform him of the origin of the 7418880 Electormagnetic Anomaly. Prior to this he probably had the Kahana team assembled and on alert, waiting for further instructions. Once Widmore had the location, he called the Kahana and gave them the approximate location of the Island. They then searched via helicopter until Naomi's helicopter found it.
Abaddon may be involved in tracking down "special people" - since we saw him with Locke in the past and advised him to go on the walkabout, and there is some mystery as to why he chose Frank Lapidus, Miles, Charlotte and Daniel, it is possible that they are also special people.
Theory 2: Chosen for practical reasons
They were all chosen because each of them is the most qualified person in the world in dealing with a specific aspect of the Island. Frank's obsession with 815 makes him the world's top expert on the subject, and similarly Charlotte is an expert on the DHARMA Initiative. Miles' psychic powers make him the most suited for dealing with Jacob/Island ghosts/the Monster. Daniel has a unique intuitive understanding of physics/electromagnetism.
Regina's suicide is Ben's fault. Ben has the ability to communicate with others mentally. In support for this theory there is the fact that Ben passed Juliet a message through Harper when he was being held prisoner by Locke and was not in touch with his people. He was able to do this because he has the ability to communicate with others mentally, for he was not in touch with The Others any longer. Ben made Regina commit suicide by controlling her mentally, because Regina was easy to control in this way, and because Ben wants to prevent the Freighter from getting to the island. Thus, Captain Gault decides to "move to safer waters," because he cannot afford to lose any more people, and Ben achieves his goal temporarily in this way.
Blood on the wall
It's Brandon's, for he is the only one we've known to die from the time distortion sickness but have not seen.
It's the blood of somebody who committed suicide just like Regina.
The blood splatter looks like a splatter from a gun shot to the head, perhaps Brandon shot himself or Captain Gault shot a disobeying crew member. It is no secret that uses extremist ways of getting to his goal.
Michael was supposed to clean up the blood, but did not so that Sayid and Desmond would see it.
The blood was left there on purpose, to deliberately discomfort Sayid and Desmond, almost as a threat.
The tapping heard while Sayid and Desmond were in the sickbay was the occupant of their future room with the nasty bloodstain. I believe he may have banged his head on the wall till he died.
The direction of the blood spray (upward cone) as well as the concentration of spatter (dense at the bottom where cone peaks) and the upward angle it sprays at suggests that someone placed a gun in the person's mouth (whether it be suicidal or homicidal) and pulled the trigger.