Possible to get positions of characters in a text layer?

Why do you want every letter on a separate layer? You can animate individual characters using one or more text animators. I can't imagine any animated text graphics that would require every letter to be on a separate layer.

If you absolutely must have every character on a separate layer, then you can use sourceRectAtTime() .width + a padding value to keep the space between letters constant and fake kerning. I'm not going to give you the expression, but it would start by looking at the layer above, taking the position of the first character, and the width + a padding value applied to the layer's position to make it work. 

Come to think of it; the expression is so simple I'll share it. The first letter would be on the bottom layer and have no expression. Here is the Position expression for each text layer above the first letter.

r = thisComp.layer(index + 1);
p = r.position;
pad = 20; // 20 pixel padding
w = r.sourceRectAtTime().width;
[p[0] + pad + w, p[1]]

The padding for a font with a point size of about 100 would be about 20. You'll have to adjust the pad for your font size. If you wanted to do the math, you could retrieve the font size from the SourceText property and divide that by some figure. Maybe I'll try that later. That could give you an animation preset that you could apply to multiple text layers.

You'll also need a way to make a space. The easiest way to do that would be to pick a character that you are not going to use, like a -. Write an expression for opacity that sets the opacity to 0 whenever the source text is a dash. That expression looks like this:

t = text.sourceText;
if (t == "-")
	0
else
	100

Those two expressions give you something like this. The position of the line depends on the position of the first character.

If you want more than one line you have to add another layer with a different position expression that uses sourceRectAtTime().height plus padding to offset the second line in Y by the height and a padding value equal to the amount of leading you need between the lines. A capital letter is going to require less padding than a lowercase letter like an 'e.' 

This is what that looks like:

I shared a project file if you want to fiddle around.