Aye, my friend is fixing her 300-400G pond today, she asked me for fish suggestions to fill it with, I suggested some dojos and goldfish. You have any suggestions for 'er?
Depends on what she's looking for. If she wants larger fish, then yeah goldfish would be her best bet. If she's looking for small fish, she could do whiteclouds.
A pond this size could fit a few koi. But there is a large number of fish she could use.
Depending on the state, you could keep some fish year round outside. But I am not sure where you are located. A good fish to try for small fish are Mosquito fish aka Gambusia. So if there is a shallow end a place for them along with a deep end for the larger carp. The more colorful fish would be seen while the smaller fish will help in insect control.