Re: apply existing styles to paragraphs

That's easy enough:

var mySelection = app.selection[0];

var paraStyle1 = app.activeDocument.paragraphStyles.itemByName("style1");

var paraStyle2 = app.activeDocument.paragraphStyles.itemByName("style2");

// etc.

mySelection.paragraphs[0].appliedParagraphStyle = paraStyle1;

mySelection.paragraphs[1].appliedParagraphStyle = paraStyle2;

// etc.