More emails do not make sense and actually do not increase your security and safety. If people don't have healthy web-surfing habits, more emails don't help them safely from potential threats, from bad guys. This is another thing beside inconvenience when someone have to log in different emails.
However, using few emails that store important things, and only for your main accounts (with main parts of your capital) is enough. Such emails should not be used for any other things. For example: Email A for exchange A should be used for only Exchange A.
Note that should not store your money on exchanges, if you don't have plan to trade or sell your coins.
I have tried this once to be honest and the results are excruciating for me because I need to switch into different emails every time one service asks for authentication and I'm logged in on a different email... It might not be the most efficient way to sort things out
21 emails are too many, and you should not expand it.
I'll stick with my 21 emails.
I don't know reasons of repeatedly email hack of this guy:
https://bitcointalksearch.org/topic/account-kenzawak-compromised-again-5165936I guess that guy has unhealthy web-surfing habits (I maybe wrong)