on your first question, i think that came up in a conversation we had with one of our customers. unfortunately i don't think it is possible. there is an enhancement requests out there for it:
Ability to display (list) the vector/stress component information for principal stresses
If you enable vectors in the advanced options, you can see the vectors and relative magnitude and direction but you can't output the components.
Regarding your last question, I think you can only output one at a time. If you want a specific node, you need to use the probe tool. Since you have to output multiple parameters are the same location, save it as a sensor first so you get the same location each time.
Regarding your more general question about predicting failure at the weld. What methods would you use if you did manual calculations? Have you checked out the weld connector? http://help.solidworks.com/2013/English/solidworks/cworks/hidd_edge_weld_connector.htm Depending on your methods and your geometry, it might be helpful. (Note, you will need Sim Pro if you don't have it already)