Reduction of DC motor noise
You should always put a capacitor across the motor terminals even if your circuit is not affected, because brush arcing creates rf noise that can interfere with other equipment (eg. AM radios). The usual recommendation is to install two 0.1uF ceramic capacitors, one connected from each motor terminal to the case. This 'grounds' the case to rf without the danger of having an exposed DC connection.
Ripple can be a problem for sensitive equipment which has poor power supply rejection, but normal filter capacitors and regulators will usually eliminate it. Another concern is the current spike and voltage dip that occurs when starting the motor. This motor has a stall current of only 390mA, so provided your 12V supply can handle that you shouldn't have to worry about it. Just make sure that the motor and its control circuit is wired directly to the power source, and run separate wires to the other devices.
Regarding your points to reduce the noise:
- Small capacitors (1 or 10nF)
That's correct, except of the mention of capacitor polarity: anyways the capacitors must be ceramic, designed for working under high frequency, not electrolytic or paper even if motor will work only in one direction. Place these capacitors as close as possible to motor, and to the motor driver if you are using a PWM driver.
Using large (1000uF+), low ESR electrolytic capacitors connected as close as possible to other sensitive equipment between their Vcc and Gnd (Anode to Vcc, Cathode to Gnd), or placing these large capacitors next to the power source itself on all of the lines leading out..
Most likely using large capacitors will only be partially effective, primarily during start/stop/reverse of motor. Better noise protection is - to make separate power supplies for power circuit and for control part even if both require the same 12V. Your p.9 is exactly about this.
Twisting and shielding the cables of the motor and physically isolating them from the remainder of the circuit.
The major cause of noise transmitting by motor (through cables and by air) is the ignition of brushes. So if your motor is not brand new please check the brushes and connector conditions, and grind in the connector if needed.
Also plan your wire topology as a star(with power supply in center) with rays (parts of your scheme) and try to avoid the making of chain contained of consumers.
Star:
consumer2 <---wires---> PowerSupply <---wires--> consumer1
Chain:
PowerSupply <---wires--> consumer1 <---wires---> consumer2
Your motor is relatively low current, so unless you have a good model of your motor, the best approach is experimental.
Leave room on your board for choke inductor. Have small capacitor directly soldered on the motor terminal. Have sufficient decoupling on the power lines that supply the motor driver.
Then try with a few values for the capacitors and for the choke inductor and measure the noise on the supplies with a scope (or a spectrum analyser if you have one).