Hi Vishnu,
Let me try to answer your questions.
Q1. Is their any advantage to go for 7.40 with oracle database over 7.30 with oracle database.(Both without HANA).
A1. Although there are some enhancements for 7.4 on an Oracle database, the real innovation comes for HANA. From that perspective 7.3 (or 7.31) could be an alternative.
Q2. Will 7.40 support both ABAP and JAVA stack, will 7.40 support Enterprise portal.
A2. Please check using the Upgrade Dependency Analyzer. However in case of any doubt, please contact SAP.
Q3. Should we upgrade the Enterprise portal also, if so should we do before or after the bw upgrade, what is the latest EP Version.
A3. Please check UDA as suggested in A2. I expect that if you have to upgrade, you will have to include it in the upgrade project.
Q4.if we upgrade to 7.30 still should we upgrade our portal.
A4. Please check UDA as suggested in A2.
Re. Dual Stack, this is the best practice now. It is also recommended or even mandatory for 7.3.
Best regards,
Sander