Niagara skeletal mesh particles

Hello , I have created a particle system in Niagara (my first time)that uses an animated skeletal mesh, that is spawned on a grid in order to create an army effect. I want the advice of an expert to tell me how to add the following 2 attributes to the particle system:

  1. Make the particles ( 3D animated skeletal meshes) stand on the ground, so they follow the height of the ground, the elevation of the environment. Attached are 100 particles spawned in a desert environment in a grid BUT you can clearly see that they are not following the ground and stand on the air like they are placed on flat ground.

  2. Make the particles be animated randomly when spawned, so they don’t appear all doing the same movement. The idea is to start the animation of the static mesh randomly. So if the animation has 1-200 frames, then for the 1st skeletal mesh particle the animation starts at 140, for the second particle the animation start at 45, and so on, in order to break the unity of the movement. I hope I made myself clear.
    Attached you will also find a screen capture from the Niagara particle system overview so you get an idea of what I have done.

If you know how to do this please share a sample.
Thank you