Create an online database for Unity 3D Game

I have a ready to play game. Need to implement a few changes in it. This is a tank war game where players compete against A.I. tanks. Game works in a team play where every kill ads up to the total score of the team. Please watch a video demo for full understanding of the game play. I need to implement following changes to my existing unity 3d gameplay. a) Team select option (button) on the intro screen. User can select a team of his choice from the startup menu screen. b) Total Team score Live Update On start on game, fetch live updated score on top of screen. When a user kills an A.I tank, it should adds up in the total score of his team and total live score should get updated on servers. When a player gets killed, it should adds up in live score of opponent team. Updated Live score should be visible to all users in all countries. c) Individual kills/deaths score: When a player kills, it should ads up in his individual kills and when player get killed, it should ads up in deaths. These stats should be visible during gameplay on top right side of screen. This data should be stored on servers and when a player starts a game again, his kills and deaths should be retrieved and his new kills and deaths should add up to his previous kills and deaths. d) Top players and player’s current ranking (button) There should be a button on intro screen for top players which show the live data of current top scores from all over the world and his current ranking.