Very well handled in my opinion. You did a great job. I've noticed that witnesses always pull out the preaching card but you brought up some very good points against that, something I could use as well.
as for the FDS, here's another discrepancy You can point out. It says that the slave was already appointed over the master's domestics in 1919 according to the Watchtower July 15, 2013 p. 22,23 Based off of Mathew 24:45 which says: “Who really is the faithful and discreet slave whom his master appointed over his domestics, to give them their food at the proper time?
Notice it says "appointed" as in past tense, already done. Now compare it to Luke 12:42 which is the same parable: "And the Lord said: 'Who really is the faithful steward, the discreet one, whom his master will appoint over his body of attendants to keep giving them their measure of food supplies at the proper time?'"
now it says "will appoint", in the future. Why does one use past tense and the other future tense? The Governing body says they were already appointed but Luke refutes that. I asked my parents and a friend of theirs this question and I couldn't find a good answer.