Help with thinking a project!

I need a little help on how to think a project i need ideas :
it is an online mobile game top down in witch you move your character to the quest location and insert a code witch you will obtain by going to the same location in real life and solve a puzzle.
The app need to communicate wit a server:

now the questions:
1 how to create a server for the game
2 need to use a login system
3 user can add friend
4 the quests are on the server how to update the game when there are new quests added
5 add friends