Questions about Place on Plane and Tracking Enable/Desable (Arkit)

Hello,
Today I had to halt production on my AR game using the pre-ARFoundation AR packages and kind of start over using the ARFoundation Package. So, I have a couple of questions:

I am using SampleUXScene as template, and what I am trying to achieve are the following:

-After I track a surface, I spawn a Surface prefab in which my game will run on top of it, I want the app to stop tracking for surfaces completely to avoid clicking anywhere on the screen and re-positioning the prefab. Basically, once the hit is done, spawn the surface and start the game, no more AR tracking after this point. How do I stop this via script? I am usually using a disable method with a custom script but I am not sure if this is the right way.

Second, with the previous ARKit Plugin, I could just place my entire game's structure under the "HitTestCube". Now, with ARFoundation, PlaceOnPlane only instantiates a prefab, what would be the most straightforward way to Start a game as soon as the Surface prefab has been spawned? One idea I have is to enable game objects ontop of the Surface prefab.
I'm new with ARFoundation and I'd like to hear from more experienced developers.
Thanks!