Police departments are generally immune from suit for arrests absent some proveable I'll-will or intent. As for the arrest, if the facts underlying the arrest are as weak as you say an attorney should be able to quash the indictment or have the charges dismissed as without factual basis.
Evading Arrest is found in Texas Penal Code Section 38.04. You can find that here:
which may be helpful to you in determining the answers to your questions. I'm assuming the information you have listed was relayed to you from your friend. If that is the case you cannot be sure how strong or weak the prosecutor's case is, as you have not seen the evidence, and if you are not a criminal defense lawyer, you do not know how to evaluate the evidence or the law relating to this case. I don't say that to be derogatory, only to point out that, much like doctors or any other specialists, good lawyers are trained and capable of determining how to advise their clients. The standard to charge someone is whether or not there is "probable cause" to believe a crime has been committed. Evidence must be presented to a grand jury, and if they find probable cause, then an indictment will be signed charging the individual. "Probable Cause" is not a very high standard and does not require very much evidence to satisfy.
Good luck and I wish the best for your friend.
The plate number is a great place to start. They probably spoke with the listed owner of the car until they got to the actual owner who probably said that your friend was driving the car. The officer's identification, even if wrong, is sufficient for a warrant to issue. (The fact that he differs from the description will create a great opportunity for cross examination and impeachment by your friend's lawyer. The lawyer will need photos of him with short hair near the time of the incident.)
It is not likely he can sue IF he wins. Despite all you hear about people getting money after being wrongfully convicted, there are immunity statutes which protect police in their jobs.
No one has to notify nor question him before charges are filed.