Does the Forester come with a tow bar preinstalled?

If not...
https://www.amazon.com/CURT-13144-Trailer-Receiver-Forester/dp/B00CLMBE5A

(Not sure if that fits your model year.)

If it's like my Odyssey, installation should take ~1 hour with a few wrenches.

Then, again, not sure if this works for your model year:
https://www.amazon.com/CURT-56040-Custom-Wiring-Connector/dp/B0031G8GME/

You'll need to install the wiring harness for the trailer. Look online for instructions, I've never had it take me more than 20ish minutes.

Go to Home Depot or Lowes for a hitch receiver and ball.

You can also call most U-Haul places and they'll do all of this for you.

When you say "smallish boat," how small do you mean? You need a decent sized trailer before it starts needing brakes...

Can anyone here recommend someone to perform hitch and brake control installation? Looking to tow a smallish boat with a Subaru Forester, and need to add a hitch ... thanks!