Does it matter which way I twist my finger?
Yes, you should twist your dominant index finger forward (away from your body), mimicking the natural motion of turning a key clockwise to start a car. Twisting backward can feel awkward and look unnatural to fluent signers.
Can I use this sign for starting a race or a project?
Absolutely! Even though the sign looks specifically like starting a car, it is the general ASL concept for 'begin' or 'start'. You can use it for starting a movie, a new job, a race, or any other activity.
Should my non-dominant hand be completely flat and rigid?
No, your non-dominant hand should be relaxed with the fingers splayed (spread apart) and the palm facing down. A natural, relaxed posture allows your dominant index finger to easily slip between the index and middle fingers.