Sounds hard to define specific metrics to define how many tags are too many.

I think most tags should pass two basic tests:

* Reading the tag alone, am I able to identify some specific topic which the question will be targeting.
* There should not be another tag that already exists which covers the same exact same topic.

For example, in the Substrate StackExchange, we have tags `[FRAME]` and `[pallet]`. While these topics are very similar, I think that these two tags do have distinct topics they are trying to cover.

`[FRAME]` can include questions which are specific to the underlying macros that we create that help users write pallets, while `[pallet]` can be used to talk about existing pallets created by the community, or broader pallet development questions.

Another example is `[polkadot-js]` and `[polkadot-js-api]`. In this case, I think these two tags represent the same thing, and ideally an administrator would go and merge these two tags.

Finally, lets look at `[api]` or `[curiosity-killed-the-cat]`. The `[api]` tag is just way too broad. You cannot easily identify what a question would cover with this tag, and probably it shouldn't exist.

Similarly, `[curiosity-killed-the-cat]` is not a real topic or category of questions, and probably needs a more appropriate tag name or to be removed all together.