Nekomata Chen, kyuubi Ran etc question

Aaaand here comes another probably-already-discussed-many-times question from me. So basically Chen is always a nekomata, Ran is always a kyuubi, Suika is an oni, etc. When do I use the tags? In most images Suika has a gourd and horns, Chen has cat ears and two tails and so on. Is there any criteria on which it is to be decided or do all the posts require this tag?
So the approximate list might be:
Chen, Rin - nekomata
Ran - kyuubi
Remilia and Flandre - vampire (well this is relatively clear)
Suika, Yuugi - oni
Aya, Momiji - tengu (Momiji is a tengu, right?)
Reimu, Sanae - miko
Marisa - witch
Cirno, Dayosei, Sunny, Luna, Star, Lily (is she a fairy?)- fairy
Ex-keine - hakutaku
Komachi - shinigami
Kogasa - karakasa
I'm not quite familiar with Ten desires characters yet, but I know there is that owl-miko, I thing the same conditions apply to her as to Reimu and Sanae.
So to sum up, when do we use the listed tags with the listed characters?

I really have my doubts about tagging popular characters with such tags. As you have already mentioned they are well known to be based of a certain creature type so tagging it usually doesn't add any information to the post.
And doing this will also flood such tags with an extremely large number of posts, frequently larger than all other non-specific_character results put together. This effectively makes those tags near useless when someone is looking for mythical creatures. Negating those specific characters from your search isn't a good solution either because of two reasons:
1. They can be portrayed as a mythical creature rather than their usual self, for example see post #970596, post #499435, post #670732, post #707870, post #383842.
2. They can be portrayed with said mythical creature, for example see post #239630, post #426488.

So personally I think that it's better to tag popular characters with such tags only if they exhibit prominent features of that creature, like examples I mentioned before.

And what about Reimu and Sanae? When are they supposed to be tagged as miko?

Only if they're wearing the traditional miko outfit that would qualify for the Japanese_clothes tag (like post #8892). Their normal attire was deemed not to qualify for the miko tag usually. Miko and a lot of other "job" tags are better referred to as "costume" tags, as they're based on whether or not the character is wearing the appropriate outfit, not whether or not that is their actual profession in canon.

Due to the the miko tag implicating the Japanese_clothes tag, a nontraditional_miko tag was also created for outfits that are styled after the miko outfit, but would not qualify for the Japanese clothes tag.

There is also the adapted_uniform tag, where the outfit may still be classified as like miko, police, maid, etc but there has been alterations that make it recognizably different from the norm.

Yeah, I think I got it. Maybe we should put it on the wiki somewhere?