Answer 1

Yes since the language used in Unity is C#

Answer 2

Yes

Answer 3

Learn the language before the framework. Use books first and for unity once you know c# fluently, use catlike coding

Answer 4

If you want to get into game development then yes. If you are learning C# for something else then you don't need Unity.

Unity scripting is all about knowing the right functions inbuild into Unity Engine to use. So if you want to make games, you can directly get started with Unity with some basic C# knowledge.

This tutorial series will be helpful
https://vionixstudio.com/learn-unity-game-engine/