The police or the victim are the only people who can press charges in an assault case.
state can pick up the charge if they want.
An assault case in the UK is The State vs The Accused, and while charges can be dropped at the request of the victim, it's not automatic. Depending on the circumstances (if the attacker was armed, whether the attack was premeditated) the state might ignore the wishes of the victim.
The police intervened at the right time and stopped the assault.
Generally not. The prosecution is in the hands of the prosecutor, and only the prosecution can decide to drop or pursue a case.
No real way to tell. The things that will influence this would be- prior charges, whether the assault was unprovoked, amount of physical damage, age, sex and condition of victim, whether charges are pressed by the victim or the crown, mental state of the perpetrator, random victim or family member, etc. Being premeditated would be a factor, too. Just in case you're planning something.
If you are not being represented by an attorney, you simply go to the courthouse and tell them you want the charges dropped. There should not be any fees involved with this.
It depends on the type of assault (Simple - Sexual - Battery - Weapon - etc) and the age of the minor. Assault is 'assault' no matter the age of the victim but it can be enhanced by additional charges of cruelty to a minor - or similar type charge.
Citizens cannot "press charges." The only thing a victim can do is contact law enforcement and report the incident and cooperate with police and prosecutors as they make a criminal charge. The victim/witness does not receive any compensation.
The entire premise of your question is faulty to begin with. Victims cannot decide whether to 'press charges' or not. Only the state has the ability to press charges, especially in a case such as you describe which involves a felony assault. Therefore: it is the state which chooses whether or not to prosecuite you and the victim has no say in the matter.
You will get off with a misdemeanor penalty if you have money, no prior convictions and don't have lots of other pending charges. The victim has not say in the case and usually ends up broke on state aid and a victim again. If you are a criminal you have rights if your a victim you just have injury. Sorry victims.
Depending on the wording of the statutes in your particular state, the charges will be similar to: "Assault And Battery" - "Threats In A Menacing Manner" - Assault With A Deadly Weapon." If any injuries were suffered by the victim the charges could be 'enhanced.' When you are presented to court, you will be read the charges against you, and you will have the opportunity to consult with an attorney/public defender before you make your plea.
An assaultee is a person who is the victim of an assault.