Ok, 2) The abdomen is a fine place to place the attention, and can lead to deep concentration, but it's also true that the tip of the nostrils is often to said to be a place where people can develop deep samadhi as well. The fact that it's a smaller area, in some cases, makes it a better object for deepening concentration. That being said, there are many objects of attention one can explore doing concentration practice. And as Daniel mentioned in another post, once concentration has been established, then it can be used to do the investigative work of insight practice. Just as when a telescope has been built, it can be used to explore the stars above. You don't have to do it that way, but insight is what leads to enlightenment.

Best of luck moving forward!