

Little bit of a nitpick but Kessler syndrome doesn’t care about how many satellites you have, and more about how many dead satellites you have hanging around on random orbits. You could put hundreds of millions of satellites in space as long as you had some sort of decommissioned program. You can always send up rockets if you can just move the satellites out of the way / know where they are.
I sincerely doubt that a collision in low earth orbit is going to result in debris being flicked up into geostationary orbits, the energy differences involved are just monumental.