How to make a team select and character select?

Hi, I’m trying to make a game which there’s two teams a survivor and a killer, just like Dead By Daylight for reference, I want people to click on a button and change to killer or survivor and when they go to a certain place they start as a killer or survivor depending on which they chose, also I want to make a max capacity for killers and survivors, and when a player is in a certain team can change for certain characters.

Thank you in advance.

Just another thing is the gamemode client sided or is it dependent on the level?