If the charge are filed and a warrant is issued within the statute of limitations period, the statute is tolled. You may have some other defenses, however. You should contact an attorney in Washington State to discuss your options
Yes, an attorney can help. The prosecutor will probably know about your previous offense if it resulted in a conviction, and of this case results in a filing it will be reflected on your record. You're a young guy; I hope you have learned your lesson this time.
Your attorney should be assisting you with this. Interestingly, there were some very recent cases on just this issue that should be reviewed before deciding to seek appellate review. I'm sure your attorney has looked into this and will advise you accordingly.
You can look up the profiles of the attorneys you are interested in here on Avvo. It is a great resource. And, as my colleague has said, most of us offer free initial consultations, so you can call or consult with them to see which one you like. Personal referrals are also a very good way to find an attorney, and you can see some of those as well on Avvo in the client review section.
The best advice I can give you right now is to get in to see a criminal defense attorney as soon as you can. There are many questions to ask to decide where you are in the process and what is the correct course of action to take. If there is a warrant outstanding that will be the first thing to tackle; you don't want to get arrested before you have a chance to speak to an attorney.
The defense does have disclosure obligations under the discovery statutes. If the evidence is going to be used at trial, the defense may have to disclose it prior to trial or the prosecution may be able to have it "excluded" from the trial, or some other less onerous remedy. Exclusion is not the same as suppression, as pointed out, but the defense is not entitled to avoid statutory procedures and sandbag the prosecutor (unless you have a very schrewd attorney and the right situation!)
It means that the DA is alleging that you have a blood alcohol of .15 or greater, or refused to take a chemical test. It probably means that one count applies to each count of DUI, and is usually alleged as an enhancement to each count. It means that the judge can increase penalties on either count if you are convicted and those facts are found true. You need an attorney to help you with this case if only because of these allegtions.