You can create division between two areas with your furniture arrangement. For example, your sofa could float in the room, facing the rest of your seating pieces. You can put a console table behind it which faces into the dining area. Without seeing pictures and knowing details like the traffic pathways through this space it's not very easy to help you further. What styles do you like? What colours? The possibilities are infinite :)

My drawing room front Window is going to be of around four feet wide. As the width of this room front wall is 10 feet out of which 3'6" will be kept for front entrance door. I am confused whether the sill height of the window should be 6 inches or 3 feet high as sofa is coming in front of it as my drawing room size is 10'0" * 14'0".

It will be better if you don't think of separating it .

For the dining room, I think I'd orient the table 90 degrees from how it's drawn, and I would make it a drop leaf or gateleg table so that it can be made smaller when not being used for dining. I would embrace the idea that the entry is right in the middle of the living room, and bring the living room furniture out towards the fireplace so the fireplace is connected to the seating area. Maybe TV above fireplace. In that back corner where the sofa is drawn, I'd make that a small work/office space.