Aside from not giving the police information that can be used against you, there are additional benefits to retaining an attorney. First, you can tell the detective that you contacted an attorney and he/she told you not to answer the questions but to call him/her (the atty) instead. That way, you can shift the pressure of having to make any decision to your attorney. Secondly, the police/prosecutor will then have to contact your retained attorney with any questions, not you.
I haven't read the other lawyers' responses, but I think you need to provide more information. At what stage is the case currently? Pretrial? Was he sentenced? Did he violate the terms of his bond? If he was sentenced and didn't use his bond money, then that can usually be applied to his total fines/costs assessed by the court. However, if the person who posted the money has to request it back and have it applied.
That's not exactly correct information. The law is "OWI" which stands for Operating While Intoxicated. Courts have found defendants not guilty in situations in which they were in a vehicle, intoxicated, with the engine running. A person is not "operating" a vehicle if it is in park, regardless of whether the vehicle is running, as long as it's not in gear. These cases are very fact specific, and it often depends on what the defendant told the investigating officer. For instance, an...
Assuming it's your arraignment tomorrow, plead NOT guilty. You will then be entitled to a pretrial conference, either on another date or after the arraignment, depending on your court's procedure. You should consult with an attorney after your arraignment, and make sure not to answer any more questions that police or prosecutors ask you from this point forward.
It's very unlikely you'll go to jail, but every court/jurisdiction is different. Assuming it's your arraignment, plead not guilty, ask for a PR bond (personal recognizance), and ask the court to appoint an attorney if you can't afford to hire your own. In the event that you are taken to jail for processing/fingerprints, you should take some bond money with you just to be safe.
DO NOT PLEAD GUILTY. Even if you don't hire an attorney (but you should), you can at least get a pretrial conference by pleading "not guilty." The pretrial conference is where you or your attorney can talk to the prosecutor about your case and possibly get the charge reduced if not dismissed. If plead guilty, you'll never get that chance.