The decision to reduce DUI charges rests on many different things. One of those may be the number of prior DUIs you have. As pointed out, typically prosecutors are reluctant to reduce DUIs if you have any priors. It's not impossible, but it can be difficult to get it reduced. You will need an attorney to try to navigate these proceedings against you.
The ETG test can test for the presence of metabolites that your uses to break down alcohol. These tests are very sensitive and can detect the recent use of alcohol. I don't know if Clayton County is using these tests or not, but I do know that some probation offices in the Atlanta Metro Area are. I would strongly recommend staying away from any drugs or alcohol if you are on probation as they can be easily detected.
The First Offender disposition won't count as a conviction obviously but many employers have begun to ask questions relating to First Offender dispositions. As mentioned above, your mugshot and media information are likely still available on the internet, not to mention the court records are public documents. First Offender will prevent a conviction but won't "make it like it never happen". Being honest and upfront about it will be the best course of action as it is likely an employer could...
Most probation officers will work with during your period of probation if you have extenuating circumstances come up (death in the family, loss of job, unexpected bills, etc.). If you don't report to probation, the likelihood of them trying to help you goes down exponentially. As for any potential warrants, you will likely need an attorney to check for you.
I would agree with the above answer, the dead docket is just a way of procedurally holding a case open. If the defendant is already serving a sentence for a probation violation then the chances of him getting out on a bond are slim. He may, however, be entitled to a bond once his probation sentence is served. An attorney would be able to tell the likelihood of these things happening once he or she looks at the files and gets an idea of how far along both cases are.
Being on Social Security Disability does not excuse someone from paying a court ordered fine. You may be able to make arrangements to make payments with the court, depending on where your conviction is.
Having charges dropped or dismissed depend on a number of things. Once a criminal case starts it is up to the government to prosecute it by way of the District Attorney or Solicitor General. At the end of the day, it will be up to them to determine whether the case should be dropped or dismissed. It sounds like there is some evidence to build a defense around and you should definitely consult with an attorney to discuss your options.
Federal sentences can only award a certain number of days or a small percentage off of the original sentence. In short, your ex will probably do the bulk of the sentence if not all of it. If this is a state sentence then the Board of Pardons and Paroles will set the parole date. Certain crimes, such as armed robbery are not subject to parole.