Dear Dipankar,
Congratulations!

The 17-40 is a great lens. You will find some good landscapes in Ranthambhore. Even in Delhi you can use it in number of places.

You are right that the 50D will feel much better in the hand than the 500D. It is a great camera. The 300mm f4 L IS is a great piece of equipment as well. Just add a 1.4x Converter if possible. I hope your wife doesn't come to know that I am giving you all these advices.

Now my advice would be to understand the limitations of your equipment and push it to the hilt. And push yourself in extracting juice from your equipment. There would be learning curve but in digital you learn fast. There are lot of good guys posting here. Pick their brains and you will benefit a lot.

Cheers,
Sabyasachi