is it monthly payments ? or 1 time purchase ?

1. it is NOT live, not sure at all where you figure that

2. it is both, $60 payment and you get 1 month alongside the game, after that it is $15 per month.

http://www.elderscrollsonline.com/en/news/post/2013/12/11/eso-release-plans-announced

Get ready to begin your adventures in Tamriel—we’re excited to announce that The Elder Scrolls Online will be available worldwide for PC and Mac on 4.4.2014 and for PS4 and Xbox One in June 2014! We can’t wait to get everyone in-game!