Hi I created a FileLoadDemo and made a pull request to to get it in HelixToolkit.SharpDx showcasing loading files. You should see it under pull request. Otherwise you can have a look in my repo were it is already merged https://github.com/SiNeumann/helix-toolkit

For the mouseposition, if you want to find if your mouse is over an 3D object you can use find hits like this

private void MainWindow_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
{
var hits= view.FindHits(e.GetPosition(view));
}

In this case "view" is the Viewport3dx