My question involves a driver's license issued by the State of: WA

I was pulled over last weekend for turning into the outside lane on a left turn. When the officer ran my license, he informed me that my license was suspended and that he was placing me under arrest for Driving With a Suspended License in the Third Degree. Before he cuffed me, he asked "Do you know anything about unpaid tickets?" I said no, I've only had one ticket, years ago, and it was deferred. He told me that was false and my license had been suspended last November because of failure to pay.

In March 2009 I received a ticket for speeding in a school zone. This was the first (and only) offense I've ever received as a driver. I was doing 12 over the school zone speed limit, but none of my passengers or I could recall seeing the flashing lights on the "School Zone" sign, and the ticket was issued after school was in session, so we were fairly sure I could argue out of it based on the fact my speeding was negligible under normal conditions. Regardless, I lived 3 hours away from the area where the ticket was issued, so we were told to ask for a deferment on the ticket. You can defer one ticket every seven years in the state of Washington, and as long as you keep a clean driving record for a year afterwards, the infraction never shows on your record (as well as keeping your insurance down). I was 17 at this time so my mother paid the fee that went with the deference, and we figured all was clear.

Somehow, the court never received my payment, so it went unpaid. I moved in July last year, and had yet to update my license with my current address. We've been getting mail forwarded to us from our old address weekly since we moved, including many important letters from various departments, but I never once received a letter telling me my license was going to be suspended. The other interesting thing about this is that my mailing address on my account has always been a personal P.O. Box, which was confirmed when I went to the DOL a few days ago. So why wasn't the letter mailed there if I designated that as my mailing address?

So now I have a court date in a couple weeks. I've already paid whatever outstanding fines are on my record, after those were confirmed to have been paid I went and got my license reinstated. Here are my questions:

1) Is it a waste of time to even argue that there was a mistake? I admit fault for not promptly updating my license, but my mailing address has always been a PO Box, which is where my suspension notice should have been sent. On top of that, my insurance company never received notice of this because my rates have not gone up. I understand that not knowing isn't a legitimate excuse, but do I have a decent reason to believe there may have been a mistake with the mailing situation here?

2) If I provide proof of my reinstated license, proof of insurance, and proof of payment for any outstanding fines at my court date, is that going to be helpful in getting a plea deal?

3) In getting a plea deal, should I even bother hiring an attorney for the arraignment? Should I just try to get a plea deal from the DA based on my clean record and hope for a small fine and reduced charge?

4) If the DA decides to refuse a plea deal, should I then ask for some sort of extension time so I can meet with a lawyer?

Thank you for all your help.