Hi Gautam,
You need to check the availability of Jungle safaris and rooms here: https://www.corbettonline.uk.gov.in/...torLogin.aspx#

Alternately you can also check with some of the hotels there. Now upmarket hotels like Taj Gateway are also there.

100-400 is light and handy and is ok for many situations. However, at times tiger sighting can be very far and even 600mm lens won't be sufficient. All the best!

Cheers,
Sabyasachi