You can feel 'guilty about' doing something, but you are 'guilty of' a crime.
Whichever court you are being tried in determines your sentence.
Yes, you can.
Up to a certain point, yes. It is not helpful to your defense, though, but if you can successfully defend yourself then it is worth the time.
It means that either the jury (or judge) found you not to be guilty of the offense for which you were arrested - or - the prosecution failed to prove its case against you. Not guilty does NOT mean...