Collection, category and tag: choice for a specific application

Hello,
I need your help in order to choose the better model for a website.

My goal:
I would like to represent in a website the fauna and the flora of my region. Fauna is a collection of animals and flora a collection of plants.
Theory:
The biologists used a model of classification but I am not a biologist !
Therefore I decided to sub-divide
the fauna in mammal, fish, amphibians, bird, reptile, insect, more …
the flora in flower, tree, more …
It is not rigorous I agree !
Matter:
My observations are posts composed of images, text and date.
Problem:
I am confuse with the terms of collection, category and tag.
Everything that’s not a post or a page can be represented as a collection BUT my observations are posts.

Could Fauna and Flora be collections and the sub-divisions categories ?
Could Fauna and Flora be categories and the sub-divisions tags ?
Could posts grouped by collection ?
etc etc

I ask myself too much questions … which model could you proposed me ?

rgds,

if you are using posts this is probably what I would do.

But keep in mind you can make any custom front matter you want, so you could have fauna and flora instead of cats and tags, you just don’t get site.cats and site.tags, though those do make it easier so I would probably stick with cats and tags.