Your system solves nothing.
In this case, if they where using your system, they would get the account number needed to write checks OUT. Since this IS a booking service. The thieves can now get cash out of your account. Are you really that worried about thieves depositing money INTO your account?
#3 Seems like some kind of check bounce protection. They already do the same thing with Credit Cards without needed an extra number. But banks don't want to change anything since they get free money from any bounced checks and check protection "services".
Anyways, I use checks so rarely that when I have to use one it takes me embarrassingly long to remember how to do it. I pay everything with my credit card. A credit card has more security, better features, more fraud protection, and builds my credit. So, why use a check?