You may need to do some research to double check these dosages but I am pretty sure that they are accurate.
For the powder- 1 teaspoon treats 4 gallons (so 1/4 of a teaspoon does 1 gallon)
Or if you have the liquid- 5ml of coppersafe treats 4 gallons of water (so 1.25ml treats 1 gallon of water, you may need to use a syringe to measure 1.25ml)
A 1 gallon bowl/tank would need 100% water changes 2-3 times a week. Each time you do a 100% change rinse his bowl/tank thoroughly before retreating.
I am afraid I no not know the answers to your other questions