The cleanest structure is: price, short rationale, financing proof, flexible completion date and a clear response deadline. Keep the explanation to one paragraph rather than listing every defect.
Make the deposit refundable while the agreed inspection, financing and appraisal conditions remain...
At that purchase price, $16,000 would feel tight to me. I’d protect the emergency fund first, reserve realistic amounts for moving and inspection findings, and treat almost all furniture as optional. A mostly empty apartment is inconvenient; having no cash when something breaks is much worse.
At roughly PLN 31,600 per m², the precise location and layout matter quite a lot. Which Warsaw district is it in, and does “5-bed” mean five actual bedrooms rather than five rooms in total? A floor plan would help explain how that fits into 80 m².
If the verified expenses confirm a very low net yield, the practical response is not necessarily to abandon the property. It may be to offer a price supported by the income. Work backward from the net return you require and see whether that price is remotely acceptable to the seller.