I have a 23"x23" SVG pattern for stained glass.  I need the pattern lines to be 3mm.  They are much larger than that.  I have tried YouTube tutorials for Stroke, 3 Inkscape books, Google searches and I am either using the wrong terminology or totally misguided.  This is the last step in my pattern prep and I could use help.  

In essence you have just a black background with coloured shapes upon it - but no lines or strokes.

Check out the file - I have added some 3mm cyan strokes:

Got it.  I truly appreciate your response.  I will get there!

To complete Polygon's answer, you could make the gaps between the shapes thicker or thinner by "offsetting" the shapes. I see two ways to do that on many shapes at once:
  - select all the shapes then use Path > Inset or Path > Outset.
  - select all the shapes then group them. Select the group and add a offset path effect to it (in Path Effects panel that opens with Path > Path Effects). Configure the offset effect: change the Offset to the value you want (e.g. 1mm) and also set the Join parameter to Rounded -  it seems to give better results on your drawing.

In the attached file, I used the second option to offset all your shapes (except background) by 0.8mm. You can change it by clicking on the "offset-shapes" group and looking in the Path Effects panel.

I had a feeling I could use offset but you have shown me the value in doing so.  Thanks so much for the advice and the drawing!