You always get the list of all active allies and opponents at the top of the screen. Using that, missing already active opponents shouldnt be a problem ?
I'm not sure what you mean. The turn order on top of the screen? I don't think that can be used to highlight where each enemy stands on the map, but then I've never messed with it.
If I recall correctly, you can click on a character portrait at the top of the screen to show that character's ugly outline. It is less of an attack on esthetics than showing all character outlines. By the way, also if recalling corretly (I haven't played in a while, waiting for things to be properly fixed), the key to highlight all works as a toggle key, so there is no need to keep it pressed, or to use a menu setting.