CUPS with +30.000 printers

Dear gurus.
My customer has more than 30000 printers (retail industry) and want to migrate the printer "strategy" to CUPS.

The first problem I am facing is they have more than 30000 printers and the second one, printing is critical.

I would need to know if someone has experience with this number of printers; if you can recommend an "initial" sizing or a tool to calculate the amount of servers/size we would need. And last but not less important, high availability.

I have been reading the forum and I found that there are stress test with 3000 printers, 10% of what I need. I don't know if I should build a cluster with high hardware resources for all the printers or if having several smaller servers (easy to restore) are a better option.

Any suggestion or light is welcome... and thanks in advance.