Am assuming that you have a High Impedance input in your Amplifier.
You could wire a 22k preset pot across your 'Hot' (red) and 'Ground' (black) wires of the circuit you have given, with the wiper then going to your Amplifier Input. This will then provide you with a control range from zero to full output.
Placing a resistance simply in series as you ask is far less effective.
Electret mic's generally have a higher output than moving coil dynamic ones for the same sound pressure level, so the pot wired as suggested will be able to compensate for this for you.
For the battery, use a switch in series to extend life when not in use and with the circuit shown AAA cell(s) should be your better option.
hope this helps
Mik