The Sprite3D node is pretty versatile. The main thing you need to do is enable the Y-Billboard flag so it's always facing the camera. When it comes to getting movement to work in 3D (with varying camera angles), it's also important to rotate the direction of movement based on the camera angle, which requires a bit of vector understanding. Otherwise they'll always move on the X/Z axis, which feels wrong unless the camera angle is dead-on.