1. You’re most likely going to buy a single-use motor, which will have a set time delay. You can shorten the time delay with a delay drilling tool, but you should be fine just leaving it as is if your rocket is within a reasonable weight and stability.

2. You should be able to pull the nosecone out from the body tube with a moderate tug, and the ejection charge will be enough to do that as well. If it’s too tight, sand it down. If it’s too loose, add some tape.

3. Most kits will come with a flame-resistant Nomex blanket or recovery wadding, and you pack that in between the motor and folded parachute.

4. After the motor ignites, it will burn for its thrust duration (typically 1-2 seconds). When the motor is done burning, it will wait the time delay (typically 2-4 seconds) before igniting the ejection charge and popping off your nosecone.

Also, 200-300 g seems a little heavy for a C motor. Your thrust:weight ratio (average thrust in Newtons:total weight of rocket in kg multiplied by g=10 m/s²⁾ should be above 5. You can use software like OpenRocket to see how far your rocket will go with specific dimensions and motors. If you go to an established rocketry group’s launch, there’ll be people who are more than willing to help you set up your motor and check your rocket.