So my 5 level Glory Paladin armed with a spear has pole-master . His Peerless Athlete is running.

Reaction: Spear Attack with both hands D8 (he got to close)

Action: full attack. first special attack: knock enemy prone. Second special attack grapple him. (speed 0)

Bonus action: Smack him with the butt with advantage (prone enemy)

Next rounds His has to brake my paladins grapple at disadvantage (prone) vs my advantage one handed grapple. RAW, PH, p. 191. “You can’t stand up if you don’t have enough movement left or if your speed is 0.” as I and the and the others pound on him with advantage.

Did I get any thing wrong?

Almost. Polearm Master only gives you a bonus action attack when you attack with your polearm. If you're making attacks with other weapons, or none of your attacks use that weapon, then no bonus action attack.

You could grapple and stab, and then get the bonus attack. Or you could shove and stab, and get the bonus attack. But you have to stab, somewhere during your attack action.

Edit: Oh, and being prone doesn't impose disadvantage on your opponent's check to break the grapple.

You are right and thank you on both acounts