SRM 7.0 Upgrade Pre-Steps

HI Sapers,

I'm an SAP Basis Consultant

Our client has planned to Upgrade SRM 5.5 to SRM 7.0(already it is been started on Sandbox), My company suddenly wants me to take up this and shadow the SAP guy who is doing on Sandbox, after which I need to handle Independently for DEV, TST, PRD

Could anyone please help me

1) what are the things I need to be ready with before we start?

2) what are the doucments we need to study?

3) Are they any question to be asked to to SAP Guy who is Upgrading in Sandbox

4) Anything if I missed out?

Thanks In Advance

Thanks

Hari