I am curious, but surely the $900-$1400 an acre is based on rows configured for tractor-based tilling/plowing, fertilizing, herbicide etc.? As I understand it, the nice thing about a smallholding is that you don't have to mechanize near as aggressively, and therefore can plant much more densely than a tractor-based farm would.

While hand grown can be denser it’s not an order of magnitude denser. The main advantage is being able to combine/layer different crops.

Look at machine farmed fields just before harvest; the fully grown plants will often be quite close together.

Perhaps? This was based on google top-link data which may not be reliable for a small farm but I assume it's within an order of magnitude!

Land prices in Portugal (away from the coast and from bigger cities) are pretty cheap for western European standards. It's getting noticed though - a quick YouTube search will show you plenty of examples of expats jumping on the opportunity.

IMO making a profit would be the hard part - the internal market is small and in general produce prices are low.

I'd be content with a small loss to be honest, I'd still be working as a remote engineer. I just would like more nature in my life!