Details:
Honda Accord 4DR LX 96'

Background:
Put some heavy box on my roof for a split second. Now theres a dent near the Sunroof.

Problem:
I live in Washington, it rains alot here. Theres a leak somewhere in around the sides of the Sunroof.

Question:
How hard is it to pull out the headliner? Also, are there directions(steps)?
If I were to pull out the sunroof to put in a new seal around it would it work?
What kind of seal should I use?
The best way to get the dent out of the roof, while the headliner is off?

Any other advice is deffinatly welcome.

Thanks.