Please help, Tripping information

[AzarahFSoT]

Here is the issue: a friend is making a trip build for his new character, some of the feats involved are dodge, improved trip, and defensive throw. Now if his build and claims are legit then awesome more power to him, however I am almost positive that it is not. However I can't find it in the rules to disprove it. He wants essentially use defensive throw as it should be as an attack of opportunity, however with improved trip it says if you trip you get an immediate attack if successful. Is he correct? If he used defensive throw and gets the trip does he also get to hit the enemy while he's down as part of the opportunity? It seemed like slot of actions for an a.o.o. If anyone has the information that I need please reply here and tell me how and where I can find it. Thank you all a ton.

~Azarah Terrafrost

[Twurps]

1. Enemy attacks and misses: Triggers defensive throw.
2. Player makes an AoO of defensive throw, triggers improved trip.
3. Playes makes extra attack form improved trip.

seems clear enough to me, and nowhere near overpowered in any but the lowest Op games.