1. They are asking for a Failover or high availability scenario, so I would like to know which components should be in a mirror state or if this should be just a Database Level.
There is an internal doc on this - at a high level, you need to mirror the database, mirror the file server and have a standby appserver, reports, etc.
2. They also are asking for the operative system prerequisites, I mean for Unix, there is no operatice system creation user or groups instructions, and also there is a specific Kernel parameter they need to take care?
The unix installer (solaris/linux) will create a OS account to run the appserver. There are no kernel parameters required, but you can run into problems if ulimits and such are set too low (I had a customer set open files to 128 which is not a good idea)
3. For the Solaris provisioning we know the customer should Install Jumpstart, but do you know which version?
Are there versions of jumpstart? It's basically a copy of the OS and the boot image on nfs and tftp.
Just run whatever is on the OS install cd.