Your coolant level sounds fine. It would usually read at a higher level when the engine has been running and would read at a lower level when the engine is cold.
I would only add Subaru coolant and/or distilled water while it's new.
On my 3.6 dipstick if the oil level is between the two holes your OK. The upper hole is the FULL level and the lower hole is the ADD level.
I believe the other engine has a different dipstick and markings.
The owners manual would answer all these questions but it can also make you
trying to find them.
Fill the windshield washer fluid, treat rear and side windows with Rain-X, check tire pressures fill the cooler and enjoy!
I hope your Son has a safe trip.