Hello Sarvpriya, 

What you want to take in your graduation should totally depend upon your interest. If we talk about Bcom Honours and Economics honours, both specialises in different fields. While bcom deals with accountancy and taxation, economics honores deals with economics and statistics. It's up to you, which course you are interested in and what you are good at. 

And about PG, you shouldn't rush into thinking about it. Take it easy. U will eventually find out while graduation what you want to chose as PG course.