Social responsibilty of the investmentMy list would include other factors such as level of activety (passive vs active), COC return, ability to mitigate risk, ability to protect principle while keeping growth, and a comfortable margin between income streams and growth.

Are the principles, ideas, and knowledge in the American market and taught on BiggerPockets applicable and reciprocal, or at least similar, to those in Europe- and specifically England? 

This simple example also ignores the principle you pay down.

I don't have any debt obligations other than my primary mortgage and a small car loan and given the lower interest rates at the moment a cash out refinance to add $40k onto my principle would actually result in my monthly payment decreasing due to the lower interest rate. 

Or use part to pay down principle on primary mortgage (I owe 217k)?

I would also include additional information about the investment objectives, principal strategies, and principles risks.

I would recommend Tim Baker at Principle Valuation here in Chicago.  

Provided all transactions are private transactions, I don't see how this would be any different (in principle) than buying a lamp from someone...

I have been talking to principles in this group for 14 months.

Basic concept is correct.However, in simple terms, after all other expenses, your depreciation would need to equal the sum of your actual Cash Fow and your principle reduction.....which would mean you have a near break even or negative cash flow investment, more so as your principle reductions increase.