A few questions from a new rider

So I finished my first bike last night and have been testing it out today and i have a few questions about riding...

1. How much vibration are you supposed to feel while riding? like when fast or slow etc...

2. I have seen some bike pictures without the exhaust pipe on, is that better for performance of the bike, cause i dont really understand...

3. my chain is pretty close to my back wheel and occasionally hits the wheel, how should i fix this?

4. When i ride i hear a sort of rattling, but i don't know where it is coming from, chain hitting something maybe? Is this normal?

thanks guys for any help, its much appreciated.

ok thank you nougat. i wasn't sure about the vibration, mine is on right it doesnt rumble in the seat but it does my hands. thanks