I recently looked at a duplex and wanted to get some thoughts on if these items should be factored into the offer price:The water heaters were over 10 years old, both gas furnaces were over 10 years old, the water was not separately metered, the front porch (cement) had some cracks in it, and both units would need some paint and new carpeting. 

Would the best way jumping into real-estate onthe side be starting with a duplex?

Previous experience went in with some partners on 9 units (4.5 duplexes). 

You should buy some condos like I do. 

Short-term vacation rentals is pretty much one of the main industries here with privately owned condos being more popular and numerous than hotels.

For instance, My first purchase was a duplex in a nice neighborhood of Dover at foreclosure; now that it is newly refurbished and fully rented, it’s a great asset, but selling at current numbers may not be enough of a return to warrant it (I perhaps over renovated) However, positioning it for a longer term hold is very suitable because of its great cashflow.

Asking for a friend - My friend owns a condo that is in a trust, has built up decent equity, and its been rented out for the last 8 months.

One individual I know has built three duplexes and a quad as infill construction.

Owner occupied Duplexes is what my wife and I are doing.  

I recently went through this with a duplex I sold for an acquaintance...we finally ended up changing the locks and keeping a key to each unit...we'd give 24-hour notice for showings and inspection and try to complete when they were at work...all according to the lease terms of course.This is a tough issue in general...keep us posted how this plays out.