Chris, contact the Houston FSDO and ask if the Flight Instructor initial must be taken with an FAA examiner. Some FSDO's have DPE's that are qualified to give the exam. However, the examiner's fee is free if taken with a FAA inspector. The DPE would charge a fee. Also ask how they assign the examiner. Most FSDO's will generate a list of several DPE's, usually three, once your instructor has signed you off for the check ride. If you must take the ride with a FAA inspector usually he or she is just assigned and you have no choice. Your CFI should know the normal routine.
Expect it to be a long day. Mine took seven hours. We spent most of the morning with me giving a complete lesson on Airspace. We also started three other lessons which he stopped once he was satisfied. We spent the afternoon going through a question and answer on most of the other subject areas listed in part II of the PTS. Lastly I had to give preflight lesson on a maneuver to be performed in flight (part IV of the PTS).
The flight occurred the next morning and my logbook shows 1.3 hours total. I was with a senior DPE. I've heard of orals with the FAA lasting as much as two days, although a full day (8 hours) is pretty normal. The national failure rate for first attempts at the Flight Instructor initial is about 50%. Try to be as prepared as possible and do your best, but no one will hold it against you if you aren't successful the first time. The FAA is careful about who they had a Flight Instructor certificate to. Remember, by design in part 61, the regulations covering Flight Instructors come after the regulations covering Airline Transport Pilots.
Good Luck!