I suppose that there should be no.

Free. But some treasure museum need to pay. most of people skip it.

Google it and All will be revealed

As for station, definitely Harajuku. I don't remember which exit it was, but Google Maps would suggest you. Regardless from the entrance to the shrine, it's easily a 10-15 minute walk.

The Shrine opens with sunrise and sunset so its hours change every month. For example, this month, December, it is open 6:40am-4pm.

Hi, so sorry for the late reply. I'd recommend that you visit early in the morning or late in the afternoon if you're thinking of visiting the shrine in the Summer. Although the shrine is surrounded by thick and lush trees, the walk from the subway to the entrance is not so please consider the hot and humid Summer weather in Japan. I think the shrine is open 24/7 but do check their website for more information. When we visited the shrine, only the main building of the shrine was closed due to renovation but other area of the complex was not. As for the stamp, sorry, I do not have any information on that.. Hope my answers could help you out & do enjoy your vacay in Japan! :)

Entrance is free.

No there is no audio guide. This is a shinto shrine which is in the tourist circuit. During my visit to Japan, I noticed that audio guides are available only for museums and declared heritage sites.

There are a number of exits. However, most enter from main entrance since that's where the car park for cars and coaches is located.