1) Non-competes are generally legal and enforceable, though there are a few states that will not enforce them. You may feel this is not fair, but the law believes it is: you voluntarily took their money in exchange for signing. You can't take their money but not honor the agreement you signed, and if you did not want to sign and be bound by the agreement, you could have refused the severance.2) The relevant state is the state you intend to work in: that is the state that will have power over your job, and so the state that will or will not enforce the non-compete.