There might be a defense to your case which will either give you a good case to go to trial on or a good case to negotiate the most favorbale settlement possible with the Prosecutor's office.
If you go to court without an attorney, the court will determine if you are eligible for an attorney with the Public Defender's Office. If so, they will represent you at the arraignment where a plea of either guilty or not guilty will be entered.
The fact you have no record at all helps, but it's...
Your detention may not even qualify as an arrest since it appears you were only brought to the "drunk tank" and released. Bring whatever documents you were provided upon release from custody and consult with a locally experienced immigration attorney just to be sure though.
Yes, he can be arrested. There are no ways around it as unfortunately the law is pretty black and white when it comes to someone 18 or over having sex with someone under 18.
All your mother can do is make the complaint to the police. What, if anything, the police and/or prosecutor does with the initial complaint is up to them. However, your boyfriend should hire the best locally experienced criminal defense attorney he can afford if an investigation is under way and not make any...
That's up to the prosecutor. The Civil demand may, but is unlikely to have, an effect on the filing decision and/or outcome of your case. The best thing to do, instead of speculating, is to hire a locally experienced criminal defense attorney who can walk you through the process.
If it was ordered as a condition of your DUI probation and you don't want to, or don't believe you have to, take it then maybe the other alternative left is telling the court you do not accept probation and serve 180 days custody (assuming this is a first time DUI). Doing so still would not help with DMV's requirement though.