Best practice for preloading web-based a game data

I'm looking for a receipt (or best practice) that can be help with the next problem.

First, I want to say that I have experience as a web-developer but It doesn't help me understand the ecosystem of Unity (as platform and how to think of).

My game contains two scenes. First scene is main menu. Second scene is gamescene. I want to do web-based game datas: translations and params for gameobjects (like, player speed and etc., It is necessary for the game designer to balance the game "on the fly"). Game data will be based on Google Spread Sheets and my should be able to to download it as csv.

Next, I want to apply this as in production as in development environments. I mean that I'd like to have next cases:

For production: game's starting and taking the datas from cache then all objects on the scene are configuring.

For development: since I have two separated scenes I may want to debug one. And If I want to debug the scene with gameplay without running gamemenu (I mean that I want to develop and debug the scene directly) I'd like to have a mechanism for live updating the game data for this scene.

The main question for me: how download all game dates, then handle their before creating gameobjects on the scene.