Without knowing any of your financial position of your work or side hustles it is hard to give you exact advice because you may be able to carry these homes until they are paid off and in that case they would provide solid returns, but there are likely better real estate investments out there.  

One solution I’ve seen is closing the purchase in cash, then securing the HELOC afterward, though this carries more risk.

Rising property values help, but make sure the numbers work with high carrying costs.BRRRR: Great strategy if you can still find properties below market value.

He sells you his house for his basis $323k carries the note.  

If you constantly chase the bottom dollar and bottom tier coverage you'll be the one carrying the most risk.Happy to connect and talk more.

Case in point, years ago we used Olympic paints from Lowes, which were carried for a long time.

I may not have explained myself clearly, so I apologize if there was any confusion.You are absolutely right that to carry out tangible commercial activities in Spain, such as real estate projects, it is necessary to establish an SL (Sociedad Limitada).

That said, working with an uninsured contractor still carries significant risks.

He didn't have to do that...you're carrying him). 

You can always charge an air and surface scrubbing fee from their security deposit after they've moved out.