everyone pls make sure you upload the game files and not the build files because if you build the game and then upload the build files how's the other developer going to open your project and expand it further.

so pls

Upload the game files AND NOT the built game files

For Unity it might be a good idea to start with a 2D or 3D core as the URP and HDRP are quite weighty.

(Another trick might be to use an older version of Unity that has all the necessary functionality)

Its going to be a real challenge keeping the file sizes down.

I have a recent game jam that clocks in at 4GB on my machine but compiles to a 300MB game.

Even chunky prefabs can take up a lot of room.

It would be better if we didn't start with lighting, as we can always install it later. Remember, the goal is to get the idea out there, with gameplay in mind, then update visuals later(or if you have the time). Besides, URP can only take a few minutes to get set up.