Thats a well put together calculation, i date say you could up it nearer €2000 with reasonable expenses.
And yes not paying Employer SS is exactly what a lot of contractors don't do and I guess is 100% wrong and illegal. Its also the reason I jumped ship when I was forced onto one of these shady LTD company contracts when I did my upgrade.
It was a step to far.
All my own opinion of course and my thoughts have zero legal knowledge or basis. I am just a pilot.