Can a mod add tags to someone else’s post?

How many tags are possible and will be shown?
I just started a movie community, with tags for actors etc already at ~30. Potentially that could increase to… hundreds? More?
How many will display? Will it always display all of them or can it be hidden /drop down, like spoiler text? Perhaps partially, e.g. the top tags are shown by default but you have to click “Expand” to see the rest.

What about tags in places other than the Piefed tags entry field? E.g. in post body, comments etc. Are they… “recognized” / “effective”?

Dammit, I had one more, can’t remember it now.