Beginner questions

[paganaye]

Hi Guys
This is not really an issue but I have trouble understanding the documentation so I am asking 3 three questions.

I am writing a game with Pixi.js this week and I am enjoying it.
Now I'd like to add a little bit of 3D.
On the photo below, I'd like the entire floor to be skewed to a trapeze while the tree, the characters and various fences stay upward.
I installed pixi3D and managed to display some 3D elements:

I can see a blank cube extracted from your getting started page.
It got me started. Thanks cube.
Then I can see a plane with a grass texture and a quad with a tree texture.
I use a StandardMaterial and set the baseColorTexture to my tree Pixi (classic) texture.
The texture was created from a basetexture that contains multiple images.
It looks like the Standard Material and quad is showing the entire texture and not the small portion of it.

So my first question is :
(1) How can I make the quad only display the top left quarter of the texture.

My second question is:
My floors are composed of 1 to 5 semi transparent textures on top of each other. Sometimes they are animated (the water is).
(2) how I can create a quad to show 4 or 5 textures.

Third and last question.
(3) I expect to display up to 2000 tiles on the screen adding more and deleting others as the player moves and the camera with it.

Does it seem realistic to you?
Do you think Pixi3D is a good match for what I am trying to do?

I am not sure you'll have the time to reply, in any case thank you for your good work.