1)ECC system is non-unicode, so does upgrade steps different for systems that are unicode and non-unicode.If so do I require to do unicode conversion before I upgrade the system.
NO. Unicode conersion is not mandatory for upgrading the system to EHP4. But if you want to perform a unicode conversion then you should go for CUUC (Combined Upgrade & Unicode Conversion)
2)Do I need to upgrade the NW version also.Currently I find documents related to NW version 7.01 for ERP 6.0 EHP4?
NO. You need to create a stack file and select the stack level for EHP4 and download the patches and kernel as per the stack.
Start the ugrade with SUM
Regards
RB