Can't tag things / write for specific console?

You can only select things that would normally show up in a search. Platforms don't.

Also, if you write a guide for a character, you'll have to manually change the URL to see them. (example)
As for objects, concepts, locations, etc., don't even bother. You can attach your guide to them, but it's impossible to access your guide from those pages. (example)

Well, it's pretty rare that you'd need to. And like I said, you wouldn't be able to link a guide to it anyway.