Project Solution | Architecture | Scenes and Views

Hello. Im new in Game Dev and new in development with Unity
(Come from Windows and Web development)

Now I want to make my first game. This will simple game (but with retrieve data from API etc.)


So I have some basic questions:

1) How to decide if I need to make new scene or build just make a lot canvases and switch between them?

In my game I see

1 scene - Loading
2 scene - Main screen with buttons--
1 button - open Store
2 button Open leaderborad
3 button - open something like map

etc...

Now I think

I need make 2 scenes - Loading and Game scene

In Game scene make some canvases
(MainState Canvas, Shop Canvas, MapCanvas, Leader board canvas etc...)

And when user clicks on button - show this canvas (its must be display like Popup)

2) If I want that map will grow up with more and more stop points (like in Candy Crush) - I need to set its to Assets Bundle and load new bundle ?

3) Best practices for Login/Authorization
I check many sites and I see that best practices for Game Authorization today - this is Google/Apple Game service and not Facebook. Right?

If I understand not correct - Can you guys give me a links what I need to read/learn ?

Thank you guys so much.