I have played a bit with addinf text layers.  Had a few problems sizeing text Photoshop seem to want to use points and a 72 DPI resolution. I also find it hard to move or align a text layer the has been added as a paragraph in some boundry, Here is some comments and code I have in one of my scripts where i playe around tryinf to do text, note several settinf lines have been commented out

/* Trying to figure out font size for the number of lines to cover the document height	*/
/* and getting setting text area to cover the document was a trip. Adobe Postscript trip	*/
/* I believe that 72 or 72.27 Point/Pica Size Photoshop Preference maybe I should see if	*/
/* I could retrieve it. Anyway mine is set to 72 Setting the document resolution taking	*/
/* the document width and dividing by 72 would probably yield number of characters that	*/
/* would fit in the document width. Setting the documents resolution comes into play	*/
/* with Photoshop text support. Using the documents height and dividing the by the number	*/
/* of lines of text I needed I hoped would yield the font size I needed. However that		*/
/* did not work the text area was correct the number of text lines did not fit. I needed	*/
/* to use a smaller font.  When the document resolution is set to 72 DPI and I set a text	*/
/* layer font size to 72 and the text area the number of pixels I want and observing		*/
/* Photoshop's text options bar there I see a one 1 to one relationship. 72 px = 72 px.	*/
/* If I set the documents resolution lower and set a Photoshop text layer font size to	*/
/* 72 px I see Photoshop scale the number to a lower number of pixels in the option bar.	*/
/* Just what I needed. Setting the Documents resolution to 60 DPI let the number of line	*/
/* I needed fit on the document. However Photoshop also scaled the text area I set down	*/
/* in size and that number of lines did not fit within that area. I needed to scale the		*/
/* text area up. Scaling the Text area up using 72/resolution did the trick...		*/

 

                    text_layer = doc.artLayers.add();                                                             // Add a Layer

                    text_layer.name = "EXIF Stamp";                                                                       // Name Layer

                    text_layer.kind = LayerKind.TEXT;                                                             // Make Layer a Text Layer

                    text_layer.textItem.color = textColor;                                                            // set text layer color

 

/* Do not set TextType to Pargarph Text for StampEXIF so action can position text layer

                     text_layer.textItem.kind = TextType.PARAGRAPHTEXT;                                        // Set text layers text type

*/

 

                    text_layer.textItem.font = fontName;                                                            // set text font

                    text_layer.blendMode = BlendMode.NORMAL                                                             // blend mode

                    text_layer.textItem.fauxBold = false;                                                            // Bold

                    text_layer.textItem.fauxItalic = false;                                                            // Italic

                    text_layer.textItem.underline = UnderlineType.UNDERLINEOFF;                              // Underlibn

                    text_layer.textItem.capitalization = TextCase.NORMAL;                                        // Case

                    text_layer.textItem.antiAliasMethod = AntiAlias.SHARP;                                        // antiAlias

 

//                    var fontSize = Math.round((doc.height- textY) / ((numExifItems +1) * sizeFactor)); // Calulate font size to use Item nomber + last \r

                    /* Calulate font size to use for StampExit keep size same for landscape and portrait base on document size */

                    if (doc.width >= doc.height) {var fontSize = Math.round(doc.height / (30 * sizeFactor));}

                    else {var fontSize = Math.round(doc.width / (30 * sizeFactor));}

                    if (fontSize<10){fontSize=10};                                                                       // don't use Font size smaller then 10

                    text_layer.textItem.size = fontSize;                                                            // set text font Size

 

//                    text_layer.textItem.position = Array(textX, textY );                                        // set text layers position in and down

                    text_layer.textItem.position = Array(textX, (textY + fontSize ));                    // set text layers position in and down for Stamp add in fontsize

 

                    textWidth = ((doc.width - textX) * 72/testres );                                        // Text width document width - offset

                    textHeight = ((doc.height - textY) * 72/testres );                                        // Text height document height - offset

/* Do not set Text Area for StampEXIF so action can position text layer

                    text_layer.textItem.width = textWidth;                                                            // set text area width

                    text_layer.textItem.height = textHeight;                                                  // set text area height

*/

 

	text_layer.textItem.contents =  "Picture  " + docName + "  Copyright \u00A9 " + Biz + " " + cpyrt
	+ "\r" + Artist + phoTime
	+ "\r" + Model  + lens + maxF + focLength
	+ "\r" + expPgm + expCmp + mtrMode + ev
	+ "\r" + wbMode + ISO  + expTime + Fstop + flshMode;

 

 

 

If your text has newlines, you must substitute them for "\r":

var text = "line 1\nline2";

text = text.replace("\n", "\r");