For reducing the number of points, I had to do something similar but for an isochrone. There were 2000 points for each isochrone and we had like 1000s of map markers. I simply picked every 200th point from the isochrone polygon and works reasonably well.

Of course, mapbox provides a parameter in the API to reduce the number of points using Douglas-Peucker algorithm. But I didn't want to make API call every single time, so we stored it and used a simple distilling depending on the use case.