Eidolon- Reach and Push Tail Slap + Combat Reflexes feat

[Raviel_Incarnate]

If I am reading these sections right, an Eidolon with Reach and Push on a natural attack and the Combat Reflexes feat (with a high Dex Bonus) can use the additional attacks of opportunity on their attack to basically push any would be attackers away again and again, preventing damage to itself while hurting the attacker?

[Raviel_Incarnate]

And as a follow-up, if it also had the Trip Evolution, could it Push, Trip, and Reach on the same attack?

[Artanthos]

Yes.

And if you had poison you could use that as well.

[Raviel_Incarnate]

What if the Eidolon also has Grab/Constrict? If it fails the grab, can it then take the Combat maneuver check to trip the foe?