Welcome (again)
Hhmm....well very approximately, there are around 250 layers -- the most I've ever seen in an SVG file!
I looked at the page you referenced and found some brief instructions. But I didn't peruse the whole page, so I'm not sure what I saw is what you want to do. It said to save the map as PNG. I think it mentioned using GIMP, but Inkscape can do it. And then use Inkscape's Trace Bitmap feature, to convert everything to paths.
What you have is not a PNG, but it does appear to be a vector file. Most of the objects are being called Symbols. While Inkscape does have a relatively new Symbols feature, as far as I can tell, you'd have to select each one, one at a time, and convert from Symbol to Group. Then from there, Ungroup, to find out what kind of object and change to path. That would take many hours, I think. I think it would be far better to create a PNG, and then use Trace Bitmap.
First, you'll want to go through all those layers, and make sure everything you need is unhidden (or if some layers need to be hidden, make sure they are).
You can use Inkscape to convert to PNG, using File menu > Export PNG Image. After you've saved the PNG, I would open a new blank Inkscape doc and import it. Then use Path menu > Trace Bitmap. Note that because of the size of the file, this could take Inkscape several moments, maybe a minute or 2, to finish tracing.
Trace Bitmap will create the paths you want, and make everything black (even if the PNG is colored). You may or may not need to tweak the results of the trace, using the Node tool. However, in that kind of image.....it would be better to find the best Threshold value for the trace, from the start, rather than tweak the results, which could take hours. I would use the first single scan option, which I think is Brightness Cutoff.
From there, you can save the file as DXF. [Edit -- Before you save. The result of the trace will be a compound path, filled with black and with no stroke. For your laser cutter, I would guess that you'll need to add a stroke and remove the fill. That can be done with Object menu > Fill and Stroke. Help menu > Inkscape manual if you need help. Or ask here, if you can't figure it out. It's not hard to do. Pay attention to the Tool Tips and the Status Bar info, for self help tips.]
I should say that I have zero experience with these cutters/plotters. I've recently taken over as admin here, because this forum was otherwise about to be closed. So I can't help much with the settings on your machine -- only with the Inkscape part.
But from my general understanding this seems like an incredibly detailed project!
Oh, and finally, Help menu > Inkscape manaul will have instructions for using the Trace Bitmap dialog. For your purpose, it's probably pretty straight-forward. But it's a complex tool, and takes some practice, for some images.
Good luck and let us know how it goes
