Firstly, congrats on your new drive Rajeev. Hope you have already fallen in love with your Vento!
WISH YOU LAKHS OF HAPPY MILES - HAPPY MOTORING.
Your car looks stunning in white.
Reading this thread made me feel bad about the VW dealership. Lets wish that they change their mentality before your first service.
In regards to the FE, I second with cooldhaya. There can't be huge deflection in the average FE meter. But, did you notice 18 when you fueled? If so, thats a bad guess. Always calculate the FE when you are about 1/4 tank complete.
For windsheild, ensure that you wipe the rubber blades with a clean cloth and use water dipped cloth to remove the dirt atleast once a day.
A shampoo bath
to the windscreen will also be great. I too had similar issues and now its all fine.
Paper is also a good method but you need to make the windscreen wet to get it done.
Also, lookout for guys who may advice you on using tobacco leaves to clean the windscreen (It gives a good result with a bad scratch on the glass).
Keep posting more details about the ride quyality, engine noise, suspension, etc.,.