Yes, it can get laggy.

I like units in woods (STW, MTW), but in the Sekigahara battle I take them out asap because of the lack of overview. I'm not used to the units yet, though I don't confuse cav and infantry. When I zoom in the units look splendid, but zoom out a little bit and it becomes difficult to tell what is what.

Camera freedom is on by default I think, so that's what I use. I haven't found the setting to use general view or restricted camera.