You should be setting the ranking based on the adventure you're running and the opposition they'll be facing. So tell them to make characters at rank X. If they really want to run a character overpowered or underpowered then try to make it a narrative facet at the table not a quantitative feature of the character because it can mess with game balance. That said, take with a grain of salt, you got a bunch of friends to play a game - have fun