I would recommend to take the train from Paris, stay at a hotel near one of the train stations and then take the early-morning train to the Airport. The area around Midi is a bit dirty (maybe a bit more than the average amount of dirt in the city), but nothing too bad. I've stayed at the Ibis near the train station and it was perfectly fine. Be sure you get your tickets to the airport the day before so that you don't have to wait in line in the morning.

If you were to go with the flight+flight, the transfer is a pain. A lot of walking (much more than any of the combined transfers between train-hotel or train-train train-plane) and lots of escalators and/or stairs. If you can't thru-check luggage, then this will be a problem, because luggage can take up to an hour to show up and priority tags are not always enforced.

Security in the international terminal can take 15-20 mins if the lines are long. The lounge has some breakfast baked goodies and good coffee so you can save some time on that.