Dear Aayush,
SAP BW 3.5 (release 640) :
Independent upgrade to ERP 6.0 EHP7 is not possible for BW system. You have to upgrade BW system along with the ECC.
SAP SCM4.10 (release 640) :
You dont need to upgrade the SCM system. Upgarde of ECC system is not dependent on SCM scenario.
SAP PI7.1 (release 710)
As per the SAP recommendation , PI system has to be the first system to upgrade and it has to be on higher release compare to other system in the landscape.
So you have to upgrade the PI system to SAP netweaver 7.4.
Also do follow the Upgrade Dependency Analyzer
With Regards
Ashutosh Chaturvedi