Service Bus on-premise - Sizing guidelines

I'm building an on-premise Service Bus, expected to handle 1,000,000 messages a day.

Does anyone have any metrics or sizing guides as to which SQL Version to use or the amount of memory and disk to give it to play with? Is SQL Server Express 2008 R2 SP1 really up to the job?

This service bus topologies page gives three different options for server configurations. Obviously the ideal is to have 3 service bus servers with a separate database, but will everything running on one machine be ok for 1,000,000 messages a day.  (we'll be using an Azure queue as a secondary failover anyway so not too bothered about on-premise resiliance)