Hiroshima to Koyasan

Hi, i've checked from Hyperdia and their recommended route to Koyasan from Hiroshima is to change to nankai line at shin-imamiya Station. However, from most of the blog, it was advisable to change from Namba station.

Therefore, my question is which one is more worth for jrpass , to transfer at Nanba station or Shin-imamiya station as i know JR pass will be covered up to shin-imamiya station.

In addition, do we need to get out from the stations (either Namba or Shin-imamiya) to purchase a train ticket to Gokurakubashi and Koyasan Station or we are alright just to change in the platform?

Thanks