The total number of deaths Macbeth is responsible for is difficult to determine because we don't know how many people died in Macduff's castle.
During the battle in Act 1, he kills Macdonwald, one the leaders of the rebel forces: he "unseams him from the nave to the chaps" (rips him open from his navel to his jaw). Macdonwald is the first man Macbeth kills although we only hear about this action; it is, however, an honorable feat done to defend Scotland. All other killings (Duncan, the king's two guards, Banquo, Lady Macduff, her family, and household, and Young Siward) that he performs or orders to be done are the result of his "o'erweening ambition" and desire to remain king.
Lady Macbeth's suicide, I believe, is the result of her own guilt about involvement in Duncan's death. Although she does speak of other deaths in her sleepwalking scene, none of these would have occurred if Macbeth had not succumbed to her belittling his manhood when she said in effect he wasn't man enough to kill the king. She wasn't by nature wicked, remember; she had to call on evil spirits "unsex" herself so that she could be tough.