Planning to start an "Online vs." Game...

Hello there, Im planning to start a game where you can play Vs. the computer, or vs 1, 2 or 3 friends, I have plenty experience in unity, but always doing offline things.
I was wondering if you could orient me in these subjects:

  1. Connect 2 to 4 players with LAN

  2. Connect 2 to 4 players Online

  3. If they are playing on the same computer, split the screen, if they are playing with LAN or Internet, follow the player you are controlling

If it is too much problem for you, dont worry, you can give me at least a few links on what and where I got to search. Thanks a lot for the help!

PS: Does a game in Android support an internet connection between 2, 3 or 4 players? I would like to make the game Multiplatform

Well, if it’s your first multiplayer project I would recommend to make like an online chat, after that make a tetris multiplayer with a chat and after that you may have the sufficient experience to make the game that you want to make!