Yes, you need to find a good defense lawyer. It would also be helpful to know what the facts are so that an attorney can assess whether there are any defenses and whether the state can meet its burden of proof. Find an attorney in your area, have a private conversation with him/her, and determine whether you can afford the fees.
Your chances on the Assault 4th Degree charge vary greatly depending on what court you are in, what you are ACTUALLY accused of doing (pushing, hitting, etc), what the attitude of the alleged victim is now, and what your prior record is for that type of offense. For the DUI charge, your chances depend on the level of your breath test, when you took the breath test (many breath tests are being thrown out now in Washington state) and what your prior record is like. One case will likely have little to do with the other as far as affecting your chances for a positive result. You should contact a local defense attorney who is familiar with your court and more importantly, your prosecutor. A local attorney will be able to give you a good idea of your chances.