Create a 2D game for Android in C#. Beginning

I want to create a 2D Android game in C#.
The game is similar to a casino.
The essence of the game:
- several reels with pictures are spinning;
- when the pictures match on two reels, the user receives a reward (additional points).


I have installed Visual Studio 2019 community
If I understood correctly, then I need to install https://unity.com/ru/download

Questions.
1. What do I need to install?
2. How much free space is needed on the HDD?
3. What should I pay for?
Or free unity solutions?
4. Where can I see the project templates that are suitable for my project?
5. Where can I get free materials (pictures and other materials) for the game?