Posters will chime in on recommended strategy but real estate is extremely localized and the fundamentals of the real estate in any given market are what should be dictating your investment strategy not arbitrarily deciding to buy single family homes vs. duplexes. 

@Rob CucuglielloYou should not expect to sort out your multi-layered situation in an online forum.

- Selling: Cashing in on the high property values and avoiding increasing costs?

There are plenty of older homes on the market that do not have closets.You need 2 egresses (including 1 that goes outside) such as a door or window, size about 70sqft (local codes may differ), ceilings at least 7ft high, and it cannot be a walk-through passage.As always, your local codes may be different.

In site managment/maintanance/rehab.

I was nearly scammed by a seller in the US who I met in person, met his "associates", toured the property with and everything, but my tip off to do more research was that he was against using a third party to hold funds in escrow even when I said I would personally pay all associated fees and noted that it would not delay closing at all. 

Highly recommend!

How important are factors like high-speed internet, furnished common areas, security features, and in-unit laundry to these tenants?

I've used APHW, if there are any other recommendations, I'm open to hearing.

Found this site and ready to explore.