Bacterial capsule vs. slime wall
According to the Wikipedia section on bacterial capsules, they're made of the same thing:


  When the amorphous viscid secretion (that makes up the capsule) diffuses into the surrounding medium and remains as a loose undemarcated secretion, it is known as slime layer.


Todar's Online Textbook of Bacteriology synonymizes "slime layer" and "biofilm":


  A true capsule is a discrete detectable layer of polysaccharides deposited outside the cell wall. A less discrete structure or matrix which embeds the cells is a called a slime layer or a biofilm.


This makes sense with what I remember learning about slime walls--the main difference I saw was that the capsule was directly associated with/only protects a single bacterial cell, whereas the slime layer is associated with/protects multiple bacteria. I'm not sure that I'd call it a biofilm though, as those are notoriously difficult to remove; their removal in hospital and food processing sysyems is a current research topic.

Regarding your three points above, I might instead argue that the slime layer provides another layer of protection in addition to the bacterial capsule.