Simple questions about DC Motor and capacitors

Hello,

I'm just playing with a L298D and a little DC motor.
I was checking the acceleration with this code:

for (int i = 130; i <=255 ; i++) {
    Serial.println(i);
    analogWrite(pinEna, i);
    delay(500); 
}

What I see is that it starts spinning when i is around 140: OK!

So I added a 100nF capacitor between the legs of the motor and I see this:

first time it starts about 160 then, after,  about 130.
Is it correct to say that the first time the power supply needs to power motor and capacitor, after that the capacitor helps to supply the motor itself ?

Also, I would like to use a 100uF polarized capacitor but not sure how to insert it.
What about if I reverse the rotation of the motor?
I think that, in this case, I can only use ceramic capacitors.

Is this correct?

Sorry if they are silly questions, just starting to learn, here! 🙂

Thank you!