To level up, you need to satisfy the customers and make them cum, which earns you reputation. You need 100 customer orgasms to advance every level. So, since you can have only 1 customer per day at the moment, you need at least 100 days to level up to level 2, assuming you make each and every single customer cum. I might change that depending on the feedback since it may be too grindy. You can track your progress by clicking on your stats in the mansion screen and looking at how big your reputation stat is.
As for variety in men, it's already here. It's just that you need to level up to unlock more customers. After all, hot studs don't really need the services of a whore, not unless it's a very special and famous one. If you've downloaded a Windows or Linux version, you can look at the game files and see all the customers there \resources\app\assets\img\customers.