If you use the search function you can find a lot of good discussion on the matter.The short answer is that they can be done, but with a lot of downside risk.  

The only downside for me is the time commitment.

The downside risk of getting in trouble is real, where the upside gain of altruism and goodwill may or may not even be acknowledged. 

You will have opinions on both sides of the spectrum and ultimately I don’t feel your going to get an answer that’s going to guide you in one way or another.I’d advise to look at potential worst case scenario and decide if in that situation you would have made a different decision.This industry is all about managing the downside and have a plan for what happens when that comes, since it’s enivitable.You will never loose money on an investment you don’t make, but on the other hand will never create the life you want if you don’t take action!  

The downside here is that property taxes are sometimes 2-3x that of properties in the boroughs.If searching in Brooklyn and Queens, I believe the best value will be in the South - Southeast sections of both boroughs.

How common is it to find turnkey providers that also will manage the properties, and are there any notable downsides?

Essentially a second mortgage.That way, you are still leveraging your equity but without some of the downsides of a HELOC.The rate is going to be higher but if the numbers make sense, you can look into this strategy as well.If you would like a recommendation for a lender that can do either a HELOC or a HELOAN, please let me know.

It is ultimately a business decision whether or not the benefits of making money using the technique outweigh the time spent and downside risk involved.

The downside to this however is that, as a foreigner, you are restricted to the number of properties you are allowed to buy in Egypt and you will also be unable to sell on the property in a period of less than five years.

You can do the same terms as if you had done a sub-to, but you just won't have the deed (that's the downside).