You need to stop talking with anyone, including your wife, about the details of your case. The only person with whom you should discuss about the details of your case is your attorney.
Are you a US citizen? If not, a conviction or guilty plead of domestic violence against your wife can result in a removal proceeding against you.
If you are a US citizen, there are no immediate immigration consequences for you. However, you may still have many legal problems.
The state's assault statutes are at: http://apps.leg.wa.gov/RCW/default.aspx?cite=9A.36 .
RCW 9A.36.041 provides: "(2) Assault in the fourth degree is a gross misdemeanor."
In WA, the maximum penalties for a gross misdemeanor are up to a year in jail and $5000 fines. First time offenders often get much less if no one is injured.
Depending on the facts of your case, your attorney may be able to work out a deal with the prosecutor so that you pay some court costs, attend some classes, not get into criminal troubles for a year or two, and get the case dismissed. Or, if the police or prosecutor did not follow proper procedures, your attorney may even be able to get the case dismissed. (The officer's checking the wrong boxes on the notice to appear will not get you very far.)
Having your wife's cooperation is helpful to the prosecutor in proving the city's case. (I'll use the word city even though the charge may be filed in a city or county court.) However, if the prosecutor has enough other evidence, your wife's testimony may not be needed to get a conviction against you.
Both you and your wife may need to review your separate facts and options with separate attorneys.
Depending on your wife's facts, she may want to invoke her right against self-incrimination that may effective prevent the prosecutor from using her as a witness.
The maximum sentence for a Domestic Violence Assault 4 is 1 year and $5,0000. There is no mandatory minimum sentence. Because you do not have a criminal history, an attorney may be able to prevent you from having to serve any jail time as well as prevent this from tarnishing your record forever, especially if your wife does not wish for you to be prosecuted criminally. The best thing that you can do right now is stop talking about the incident, attend all court hearings, get an attorney on board right away. You should also think about getting a domestic violence evaluation. If you have further questions feel free to give me a call.