It depends on the county and whether your case started as a misdemeanor or felony. If it was filed as a felony in Dallas County (and is being reduced to a misdemeanor), you're going to do a full PSI an d possibly a full CATS evaluation. During the PSI they will interview you about your upbringing, your educational background, your work history, your social life, and the offense itself. It's important to be honest about the offense at this point. If a judge sees inconsistencies or the interviewer says you are minimizing your responsibility, she may bust (refuse to accept) the plea. Nothing you say at the PSI could be used against you in a trial if the plea fell apart. CATS screens you for alcohol, drug, and mental health issues. How honest you are in this interview is another story. They are recommending inpatient for a lot of people these days. So the more you admit using, the more likely this is to happen.
If the case started as a misdemeanor in Dallas County, you will do a brief orientation (no PSI or CATS). They will make sure you understand the various conditions of probations and assign you a field officer. You will also have to take a reading test (but you can skip this if you bring a high school diploma or proof of GED).
If you have any additional questions, you should ask your attorney directly.
It depends entirely on the county where you were placed on probation. Each county has its own procedures. You can expect for them to get very detailed information on you, your residence, your family, your job, your friends, etc. You may be drug tested.