Tilemaps best practices

Hello everyone, I'm pretty new to Unity and I just finished some courses and tutorial found in the official documentation and I'm now in the process to apply what I learned so far using different assets from the ones provided with the tutorial, to see if I understood all the material.

I'm trying to build a simple top-down game with some free asset I found online.
My tile palette is composed, among others, of tiles like these:


In order to have something like this:

(sorry for the quality, I recreated it in gimp since I'm not on the computer where I have Unity now)

I had to create three Tilemaps under the same Grid. The botton tilemap containing the grass (sort order -2), the middle one containing the fence (sort order -1) and the top one containing the house (sort order 0).
My first question is: given the tileset I have, is this the most efficient way to obtain what I needed?

After having solved this problem I wanted to add a collider to the fence and to the house, but since now they are on two different tilemaps I cannot use a composite collider to optimize the collider's layout. Is there another way to do this in a more efficient way?
Instead of using tiles for "interactable objects", should I use "proper" game objects instead?

Thank you

 

Thank you very much.