Raj,
The responses to your post depend entirely upon questions that will only be answered LOCALLY at your site, during fact finding within the project itself.
First, download and study the upgrade guide. In this guide, SAP describes what your technical choices will be, with SAP's recommendations. For SCM 7.0, the various guides are found here
Other versions (e.g. EHP*) are found in the same general SAP Service Marketplace area. Make sure you consult with your Basis team before making any plans, since they will probably have input as to the best way to proceed FOR YOUR COMPANY.
For a high level descriptions of new Application functionality, please refer to the Solution Browser http://solutionbrowser.erp.sap.fmpmedia.com/
Best Regards,
DB49