Hello Phi,
First let me say that Blocker was not designed to operate in multi-tenant environment. Here are your answers:
1. Several thousand
2. Reports are consolidated can be filtered by domain. However, if you are looking to send individual reports on a per-domain basis the system cannot generate those.
3. I believe the quarantine can be limited to a certain size but due to space limitations on the appliance I believe you won't be able to have more than four quarantines in total.
Best regards,
Jonathan