First of all the best advice I can give you is do not write anymore letters to anyone. As for getting into trouble for writing the letter about blowing into the BAID device you most likely will not get into any trouble because you were telling the truth. Furthermore you did not make any false police reports or obstruct justice in anyway.
I am assuming that you received a conviction because in your question you stated you had probation. If it is a conviction you can have it sealed but I doubt you can have it expunged. Keep in mind if sealed private entities may not be able to see the criminal charge but legal agencies can see the charge.
The possible penalties for possession of a firearm vary in Illinois. If you are charge with agg uuw it is non probational and you are looking at 1-3. If you are charged with uuw by felon you are looking at 3-7. Talk to an attorney because there man ways you can challenge a gun case.
No they can not search your home. Giving law enforcement consent to walk into your house does not translate into consent to search. Whenever consent is given law enforcement must not go outside the scope of that consent.
If a deal can not be reached with a prosecutor there is a number of things that can be done. The defendant's attorney can submit a mitigation package to the prosecutor'z supervisor and see if that produces a result. In some counties you can enter into a 402 conference before an agreement is reached so the judge can suggest a disposition. Also one can enter into a blind plea and the judge will sentence the defendant although I don't suggest this route. Other then the above mentioned avenues the...
You can not file a motion to suppress at preliminary hearing. A preliminary hearing is a hearing conducted to see if there is probable cause to charge. In most situations will not be allowed to go into topic regarding the search of your home. If you would like to discuss further call me 3129293171