Hashem keeps counting the Jew's because they are his Children and so dear to him and they are treasures. The method used to count the Jew's was every man from the age of Twenty year's old donated 1/2 a shekel which was counted by Moshe, Aharon and twelve head's of the tribe. The tribe Levi was not counted with the other's because the had not worshiped the the golden calf (they did not die in the desert.) The tribe Yehuda was the biggest with 74,600 and tribe Menashe was the smallest, with 32,300.The Mishkon was in the center of the camp. Moshe,Aharon,and the Kohanim Camped outside of the Mishkon,and the families of the Levi,Gershon,kehas and Merari camped around it.