The link that you tried didn't set CRS so when you import the shapefile into QGIS. It's incorrect.
If you know the CRS is EPSG 4326, then you can set it while creating the shapefile like this:
from osgeo import osr, ogr # import osr, ogr
sr = osr.SpatialReference()
driver = ogr.GetDriverByName('ESRI Shapefile')
ds = driver....
Do your vectorial shapefiles have the same shape type? i.e either “Point”, “Line” or “Polygon”? If so, you can merge the shapefiles of your vector data into one shapefile. Here is an example.
Then you can export your shapefile as .csv.
Welcome to the site. If you don't already have one, you will first want to create a vector layer that matches the extent of your largest map layer.
You can right click the new layer in the table of contents then and go to "Save as" then save as Autocad .dxf file.
Depending on the type of CRS you are using (i.e. projected or geographic) you may need to ...