Exporting Sheet metal part to 1:1 DXF File.

Just flatten the Piece then place a sketch on top then export the sketch as Dxf you can even export your Format.

Can you use a bigger template (A1 or a0) or no template at all in order to fit t he part and flat pattern at full size?

I have to use a template to specify material, quantity, finishing etc

Export files using A4 format with a 1 to 1 Dxf.

you just scale the parts to fit on the Drawing

From part model window right click on Flat Pattern.
Save As... select format to DXF.
Check DXF properties by your requirements.
No need to catch flat patern from idw drawing either from any sketch.