Question is, what motivated you to set up a Asterisk box in the first place. A review of that should answer your questions on what it will do for you.
As far as how to set it up for one softphone or many, got to this web site www.elastic.org
, click on "documentation" and on that web page scroll down til you see a title of "Elast Without Tears". Read that, it is not AsteriskNow, but most all of the PBX systems of this sort use Asterisk as its base with FreePBX included. This writing will give you a lot of info on how to set up what you need and will also open you to other uses.
Hope this helps, it should save you (and us) a lot of time trying to research what its all about.