It depends on the year. At one time it was rated 2400/200#, but the current generation is only rated 1500/150#. And yes, sometimes special equipment, like a transmission cooler and trailer brakes
are required for the maximum rating.
Best way to get complete, accurate towing information is to google something like "2016 Subaru Forester Owner's Manual." Download the PDF and read the section on towing. Everything you need to know is in there. Nothing a dealer tells you can alter or override the manual, and many salespeople are sadly uninformed.
Best wishes sorting it out!