Okay I’ll make this quick (getting late for a party but I really want some help in this matter).
I’ve got a model prepared in blender and the materials have been set just right to get the 2D look. What’s lacking now is the outline width. Of course, I can simply go to Render > Post Processing > Edge, it’s got a threshold meter, but there’s no option to help me adjust the outline width. Thing is, I want it less.
Any help in the matter would be greatly appreciated.
I´ll make it quick too:
No 
It´s been asked lots of times and I don´t know why we don´t have the feature yet, but you can not set the line width.
Ah dang! I was really hoping for it. 
I suppose I’ll have to do the linearts manually using Synfig. Nevertheless, a friend of mine did give me a simple advice (but not really resource friendly):
“Hmm, perhaps render a larger image then scale it down will make the outline look thinner.” <— by utunnels
Reason it’s not resource friendly is because I’ve got fire particles in the project. xDDD
You could try with the compositor.
You can setup a renderlayer only rendering the lines and one rendering everything else.
IIRC there is a “shrink” type modifier… I played around with it once but then threw the idea because it was cumbersome and at that point the compositor was alien
I went with making node materials that had a toon shader and looked like outlines and compositing over the actual stuff… very dirty solution.
You could download a build of Blender that has Freestyle enabled from graphicall.org and use it to render outlines.