In a pond of 160 gallons we would usually recommend 8 goldfish max
with filtration going on the rec.ponds rule of thumb of 20 gallons per
goldfish. Some folks will tell you 40 gallons per goldfish. Bigger fish
would require 1000 gallons to start with and 100 gallons per fish as
a rule of thumb. (Experienced pond keepers can fiddle with these
recommendations but they are also very good at filtration.)

In nature smallmouth bass eat crayfish. They also eat other smaller
species of
fish and aquatic insect larvae. They can survive in water tempertures
up to 75
degrees. Any higher, for an extended length of time, and I think they
would get stressed.
Probably depends on where in CA you live. A lot of temperature
difference
between say, Palm Springs and San Francsico.

Usually the smaller the pond the harder it is to filter with plants
only.
Smaller aquatic ecosystems can get out of balance quicker than larger.
Larger bodies of water are more forgiving.

My recommendation for 160 gallons is to leave it a nature pond, stock
with
plants, a couple of minnows, some crawdads, invite anybody else to show
up and
enjoy.

Learn to run it, test the water with a test kit you can get at
any store that carries fish, see what the water temperature does over
the summer,
if you can keep it from turning green (the more plants the better),
the cleaning of the rocks if you decide to keep them and
then do what we all do. Dig more ponds! Bigger, deeper, more elaborate.
Take
over the yard, give up mowing... ;-)

kathy