My on-the-spot estimate: 50,000
Police estimate (Haaretz): 50,000
"Settler leader" estimate (Haaretz): 100,000
JPost estimate: "tens of thousands"
Arutz Sheva estimate: 250,000
I assume one of those estimates is less reliable than all the others.
Best thing: no political position was expressed - it was basically one long quasi-selichot service
Worst thing: Chabad got some words in from their rebbe and the statement that "the geula is already here"