Yes you can cancel an instant booking by saying you are not comfortable with the guest. I think you can do this up to 3 times.
Refunds for guest cancellations depend on your cancellation policy
You will see money for a stay released the day after check in. It can take up to 30 days for your first payout after which it should get to you within a week
Your questions suggest you may need to do some more research on how Airbnb works......