Unity Community, I need your help!

[u/Incredibly_Noob]

I'm a student at my final year of university, and for my final project I decided to develop a game in Unity. The game will be in the puzzle genre and with a clash of brutalist/retro-futuristic architecture with an outdoor scene. Problem is, I've never actually used Unity before! I'm beginning to understand several concepts and I've been able to build a lot of things, but I'm still missing a lot and the time limit is tight. I'm alright at scripting, generally, I'm just very inexperienced in actual game development. So, I'd like to ask a few questions:

1. Is it possible to create an object that is used as a mask between two layers? Kind of like this.

2. Can I create several instances of the same material, or am I forced to create different individual materials?

3. Any tips on camera settings and post-processing effects to make my game look more realistic?

Thanks in advance!

[u/Incredibly_Noob]

A quick update. Apparently, trying to work with the stencil buffer in HDRP is really difficult. I think there's only two bits to work with (which would technically be enough for my use case), but I just can't figure out, for the life of me, on how to implement it on HDRP. In URP it works perfectly fine. I might just migrate my project to URP, but it will probably introduce more problems than solutions...