Suggestion:
* `amenity=townhall` on a closed way around the "entire premises". You could add a `barrier=wall` tag too (maybe on a separate way, so you could add area=no to make clear that it is no area, although this would not be needed for most renderers, I guess).
* If possible (aerial imagery suffuciencent): Add the single buildings as usual (with `building=civic`).
Do you mean this with your option 2? Then the rendered map (the one you are looking at) should be improved (and not your tagging). On the "Humanitarian" map this is rendered as a symbol in the middle of the area. [Example](https://www.openstreetmap.org/way/146324989), [Example 1](https://www.openstreetmap.org/way/146324989), [Example 2](https://www.openstreetmap.org/way/49781808). As far as I know the standard map has recently got a style update regarding those symbols, maybe those places would soon also show up on the standard map. Update: ah, now the icon appears at my first example 1 on zoom levels 17+ and at example 2 at zoom 18. So, you picked out a nice example of where just mapping/tagging "right" is the best way (instead of doing it somehow else, just because one map does not show it otherwise).