When you want to build the team, it is obvious that each team member should be strong in a different aspect. You should be having different resources or treasure with each account so that they could be used strategically while attacking the enemies. If you think you could not manage creating those many accounts and possess resources you could always rely on the alternative solutions. You could request your friends to join you from the beginning stage but usually friends would not listen to you as they would have different interests on different games. So, you could rely on the accounts that you could buy.
Though you may be honest in playing the game, there is nothing wrong in buying the league accounts for sale as they are also hand leveled and not managed by bots. There is no risk of these accounts getting banned. Since these accounts would stay active for a very long time depending on how you play using these accounts you could manage the team as a whole. When you are happy with the accounts that you buy then you could play the game continuously without having to worry about your friends joining you or not. However, than playing alone you could introduce this game to your friends by talking something great about the game.
Once your friends are convinced with the game and the accounts that you bought they would never leave you during weekends and other public holidays. Of course, you could play the game late night also like everyone in this online gaming world are doing. Since there are many characters in the game you could choose the roles while buying the accounts and could also choose how many champions you want before you place the order online.