I answered some of your questions
here
.
It is easy to make 4% HCL from your 5% and you should if you are going to make CDH according to the original McRae-Lackney recipe.
Use the fourth calculator changing units to Percentage (%) at
endmemo.com/bio/dilution.php
Droppers are notoriously unreliable to accurately dispense liquids. I have had droppers that varied 100% between two of them. You can calibrate your dropper using a 1 ml syringe and even use a 1 ml syringe to dispense drops. Using a standard of 24 drops/ml of solution, each drop would be 0.042 ml. If you use the standard of 20 drops/ml, then each drop is 0.050 ml. The latter is 20% larger than the former, meaning your dose will be 20% stronger. In the past Jim used 24 drops/ml, but may have changed to 20 drops/ml today.