From Osaka to Mount Koya?

Hello,
I'm travelling to Japan next spring, and I decided to stay at a temple in koya-san, as recommended by many guides.
I did some research but I still don't quite know how to get to Koyasan from Osaka. I'll be staying near Namba station so if there's a possibility to get the train from there it would be great.
I have another two questions:
Where do you buy the ticket in Namba station? Is it at a ticket machine or do you have to go to a ticket sale where a person sell it to you?
Also, I heard that from Gokurakubashi station you need to get a cable car to the top of the mountain. How does it work? Is it at the same station? And where do you buy the ticket?
Thank you very much!!

You can buy Koyasan World Heritage Ticket either at Nankai Nambai or Shinimamiya stn.
At one of these 2 stations, catch the Nankai Koya Line (NOT limited express) to Gokurakubashi. From there, take a cable car to Koyasan. From Koyasan, take the bus to the temple.
http://www.japan-guide.com/e/e2358_012.html
http://www.nankaikoya.jp/en/stations/ticket.html