Nice guide! You can also use ce_localplayer_track_spec_target 1 to set the localplayer target to whoever you are spectating automatically - however this does not always work properly so where it is more convenient, the method you mentioned is more reliable.
You can use "mirv_input camera" to move the camera while the demo is paused in order to set keyframes apparently, although I don't use HLAE and didn't use this method when I did so I do not know for sure.