Good questions.
Here's some answers.
1. Four foot visibility is absolutely normal for winter ponds. Plankton production is minimal, that's why water is clear.
2. Feeding is for larger fish, fingerlings on up to full grown adults. Fertilizing feeds newly hatched baby fish. Fertile water also effectively blocks sunlight from penetrating the pond bottom, minimizing areas where rooted plants can grow out of control.
3. Your flow is not too much to be able to fertilize. Visibility will be your key.

Teach a man to grow fish...
He can teach to catch fish...