This is where I am at the moment, a lot better than before and no double lines.
I have got the dxf file size down from 39MB to about 9MB but still need to get lower, took ages just to open it with CAMBAM.
I stopped the conversion to Pollylines after about 40mins or so and back to trying to get a smaller dxf file.

The image is only 200mmx150mm so should not be that big, should it?

Click image for larger version. 

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