I don't think you need Trickster's Blade, since the OA happens before the movement that triggers it -- when the enemy is still two squares away.
That is a pretty amazing combo -- I just hate giving up the greatspear for a glaive, since you lose +1 to hit and Rain of Blows.
It really depends on how you interpret when Polearm Gambit kicks in. The feat itself states that it triggers when an opponent
entersan adjacent square, not when an opponent
leaves as square. To be entering a new square, the opponent would have to have already, then, left a previous square. Even though OA's are essential interupts, I'd argue that the opponent is thus no longer two squares away when you use Footwork Lure as there is no such thing as being "in-between" squares in 4th Ed. By entering the adjacent square, the opponent is no longer in the non-adjacent square anymore when the OA triggers. Furthermore, nothing in the above combo is going to stop the opponent from entering the adjacent square and without Trickster's Blade, you will only be sliding the opponent 1 square.
Now, if Polearm Gambit triggered when the opponent
left its square, then I'd be inclined to agree with you as the opponent would still be 2 squares away when the OA hit.
Still, as I said, it depends on how PG is interpreted and if you're group plays it differently, then you get to save a feat and some MAD!
As for glaive v. greatspear, being an elf mitigates that +1 loss and since this combo works as an OA, getting Wis to hit more than makes up for it. If you want to prioritize damage, make sure to be a Pit Fighter and pick up Marked Scourge for 2xWis to damage. Heck, be Dragonborn to grab Draconic Arrogance for another +Str to damage and multiclass Ranger for Master of the Hunt for another +Wis to damage. Suddenly Footwork Lure 2d8+2xStr+3xWis and knocks prone even before figuring in magic items. That'll teach badguys to come near you!