it is fine and dandy to know various pronunciations of a word. Once you acquire the ability to predict stress and to pronounce it, it is not worth pondering about the questions you have raised. Instead, focus on suprasegmentals, which 99.9 percent of books dont discuss much: it is one thing to say that there are various intonational patterns, but another thing to perceive and produce such patterns. Here, you need help from voice trainers: this field is dissociated from standard accent reduction books like Ann Cook's.