Hi there,
1. If you booked online, you can get "online ticket" which is not by paper.
You only need your mobile phone and the screen ( must be online ) which you can show when you aboard.
And you can take bus from Kawaguchiko station or FujiQ whichever it's convenient for you.
http://bus-en.fujikyu.co.jp/highway/detail/id/38
2.Busta Shinjuku's ticket office is on the 4th floor.
Office hours are depends on which online company you booked from, please see below;
*with staff
・High way.dom(5:50~23:55)
・Highwas bus net(6:20~24:00)
・Hassya alright net(5:50~23:55)
・Limousine bus(1st bus~22:50)
*vending machine
・Highway.com(5:00~24:55)
・Highway bus net(5:00~24:55)
・Hassya alright net(5:00~24:55)
・Limousine bus(始発~25:30)
Both accept credit cards.
Unfortunately, there's no office at Narita airport. (Haneda has)
But as I described above, you can get the ticket online and no need the paper ticket, so that you don't have to show up to pick your ticket up at the office.
Only in the case if you can't be online, you might need to show up to book & get the paper ticket.
In that case, others will be able to go and take yours in stead.
Hope this can be your help