You can definitely pay using your AmEx Plat card for the 5x points and travel benefits. You can book using the web site if you're lucky, or directly with the first airline in your proposed booking, or with any other OneWorld airline, although they may insist on their flight code being used for a long-haul flight in the booking. You can also book with a travel agent. I have an AONE4 starting in Tokyo that I'm trying to ticket that AmEx Platinum Travel is working on; they sent it to BA to be priced five days ago and still haven't gotten a price, but if ours is simpler they may be able to book it quicker. For a business class RTW, I would try to get Alaska Airlines to book it, as they may charge lower fuel surcharges.