Seamus, welcome to pond boss, and good luck with your new pond.
As has been mentioned check your ph to see what is necessary and ag lime can increase your ph but if your water inflow is too great it could be a waste of money.
If the ph stays above 5.5 your trout should do fine cause I don't think you expect them to spawn, and the 20ft. depth should be good for the winter, but you'll need to monitor the summer temps. If you get a temp meter with a wire probe you can monitor the pond temps below 5ft.
One more good piece of equipment would be an aerator to help increase dissolved oxygen.