Naruto had almost of chakra brom the Bijuus prior to Obito giving him the final pieces he required, Ichibi and Hachibi. With Naruto getting these two pieces plus a half of Kurama again, it was just putting the final pieces to the puzzle.
He can because hes part of the jinchuriki dimension. I can't remember the exact name but its like the same place that all tailed beat's jinchurikis met naruto during the obito fight. So apparently all of them can talk to him.