Prior to being charged for grand larcency for misuse of company credit card, if I start restitution what could possibly happen to me?

Starting restitution does not negate the possibility of being arrested, so what can happen to you is that you can still be arrested, prosecuted and possibly convicted of felony charges, which may result in jail time.  This possibility exists with or without starting restitution.  However, the State may be able to use your agreement to pay restitution as an acknowledgement of guilt and it may help them prove criminal charges against you.  I would retain a good defense lawyer before agreeing to any restitution.

You could be convicted and go to jail, even if you start restitution, if charges are pressed or the authorities otherwise become aware of the crime: a person can be convicted for having committed a crime  even if he or she then provides restitution or otherwise undoes the harm done. That said, restitution will typically count heavily in your favor in the criminal proceeding; the prosecutor may decide to drop the charges, or agree to let you plead to lesser  charges, or the judge may impose a lesser sentence because you are providing restitution.