Upgrades are only available on United/United Express flights except on Lufthansa and ANA flights booked in certain fare classes and using GPUs (Global Premier Upgrades), which are earned with 1K status. As a Platinum, you won't have access to upgrades on flights operated by ANA (with the exception of Star Alliance mileage upgrades for fares booked in Y and B classes). Complimentary (free) upgrades are only available on select routes with United. In terms of lounge usage in NRT, you'll have Star Alliance Gold (*G) status for being Platinum and can use any of the lounges indicated in the lounge finder: Lounge Information - Star Alliance - Star Alliance. I'd suggest reading through the United forum and looking at the benefits on United.com to learn more.