If you are going to be charged it will either be as a class B misdemeanor Terroristic Threat or as a 2nd degree Felony Aggravated Assault with a Deadly Weapon. In Texas you are free to possess a firearm in your vehicle at all times without any specific license as long as it is not openly displayed and you are not otherwise committing another crime (other than a Class C offense.)
Just showing a weapon to a person in a threatening manner (ie: I could use this if I wanted to) even without pointing it at them, meets the elements of Aggravated Assault with a Deadly Weapon. I have seen many individuals charged for doing exactly this.
But you are authorized to use non-deadly force to protect your self or your property if reasonable. In some cases you are even authorized to use deadly force. Given your description of events it seems clear to me that you were authorized to do what you did in self defense, but there are two problems. First, self defense is an affirmative defense that legally cannot be raised until trial. So the police and district attorney's office have probable cause to arrest and charge you and put you through the ringer. The second problem is that your version of what happened isn't the only version they are hearing. These witnesses saw whatever they saw and you can expect the complaintant to have a very different version than yours.
I agree with others that legally there is nothing to be gained by speaking to law enforcement, but practically there are certainly non-legal benefits. In a case like this where there is probable cause but a strong argument for an affirmative defense, all you are trying to do is convince the police and/or the DA to use their discretion and just not charge even though they could. Often you giving your side of the side of the story through an interview is the only way to make that happen. You absolutely should NOT just go in and speak with the police. If you are considering giving an interview then hire an attorney and let him or her decide whether to do an interview and then have him or her accompany you to the interview. Giving a prepped and controlled interview with law enforcement can often save you the trouble, expense, and and embarrassment of being charged and having to bond out, pay extra attorney's fees, etc.. all to just have the case dismissed later on after your side of the story gets presented to the prosecutor through your attorney.