A set of books can be written and in fact has been written to address the questions you ask. The best advise I can offer is to contact a local personal injury attorney and he or she can explain any remedies you may have under contract and/or tort law.
You should seek help of an attorney to fight this. The fact that you are not being charged with a DUI is good but this can stay on your record and still have consequences in your future. My colleague is correct, don't ignore this.
It is illegal to work once your work authorization has expired. The answer may be different If you have properly filed renewal and it is currently pending. In many cases, the duration of the work permit is the same as your duration of valid stay. You should seek help from an immigration attorney.
The immigration attorney who is preparing to file your petition is the best person to ask this person because he or she understands the strengths of your petition. You may be able to present other supporting evidence. It may also "help" to seek letter from a colleague who is familiar with your experience in specific occupation. Again, the attorney preparing the petition on behalf of your client should be consulted.
Police can setup roadblocks for many different purposes as long as it is done fairly, meaning either everyone is stopped or a predetermined and constitutional pattern of stopping drivers is established.
There is not much you can do if you were stopped and then let go. If you were charged with a crime after the stop, then you should ask your question in the criminal law section of this forum.