mcdirector i know what you mean.
it would frustrate the hell out of me when harry was not told these things, esepcially like sirius being his godfather, things like that which should have been done earlier.
but dumbeldore was wise.
i dont think he could see into the future, from what we know he never attempted to say he had any 'seer' in him.
however with his skills in legilimency and occulemcy, he was able to know a person's true character, and the assumptions he made about the stories that unfolded, he was able to have some sort of idea .
knowing ron would leave harry and hermione - to leave him the deluminator, knowing hermione would slow harry down and help him figure out the path of harrows vs horcruxes.
above anything it came down to his outright trust in harry.
he had to belive in harry , he knew harry would still be seeing voldemorts thoughts, which lead harry to clues.
it was all basically a quest. he had to find clues along the way. krum had observed the logo on lovegood, which eventually lead them to hear the story of the dealthy hallows and so on.
and if all else failed, there was snape to help, with his patronus or im sure in some other emergency