air shocks can be used with an explorer as far as i know.  as far as
my trailer though.  i was hauling about a ton that day... assuming
that each hay bale was 40lb (we had 50 of them).  so if you figure
that with your 10% rule of thumb, that's at least 200lb on the
tongue.  also, there should be a load rating on the plastic trim
around your bumper hitch.  my 2000 Explorer Sport says "350lb maximum
tongue weight, 3500lb gross trailer weight".  and there should be more
specific information on the inside of your driver side door (on the
label below the latch).  there should also be towing information for
your specific model in your manual (pages 181-185).  all you have to
do is match your drive-train, and engine with these charts and it will
tell you the GCWR (Gross Combined Weight Rating - the total weight of
the vehicle, passengers, cargo, trailer, and trailer load), as well as
the Trailer Weight Range
my explorer is a...

4x2 automatic transmission (page 183)
4.0L SOHC Engine
3.73 rear axle gears

so....the manual says that....

my GCWR is 10,000 pounds and my Trailer Weight Range is from 0 to
5,940 pounds
that means that the total load of my explorer and trailer together
should not exceed 10,000 pounds
and that i can tow a trailer that weighs up to 5,940 pounds (assuming
the explorer, passengers, and cargo do not weigh more than 4,060
pounds, as this would exceed the GCWR of 10,000 pounds, when combined
with a 5,940 pound trailer)

as far as tongue weight goes, the recommended tongue weight for the
bumper, is printed right around your trailer ball, and as i said
earlier, the maximum recommended is 350 pounds so you should be in no
danger by towing 320 pounds.