You will arrive at Terminal 2 of NRT and depart Terminal 2 of NRT. If you want to stay within gate/transit area then you need a boarding pass or an itinerary showing that you are departing a flight from Terminal 1 to get on a terminal transfer bus to Terminal 1. There have been reported cases where a passenger were able to transfer between Terminal 1 and Terminal 2 gate side without showing such documents, but those are more of exception than norm. I will not count on that.

If you want to go to Terminal 1 then you have to go through customs and immigration at Terminal 2 and come out on land side, then take an intra-terminal bus to Terminal 1. Obviously, you will have access to only land side facilities at Terminal 1, you will not have access to post passport control area (gate area) of Terminal 1. I think this is perfectly doable on 5 hours transit. I just want to make sure you hold a passport which allows visa waiver entry to Japan. If not you will need Japanese visa to do this.

As for lounge access, as AA platinum you will have access to Admirals Club, JAL Sakura Lounge, Cathay Business Class Lounge and Qantas Lounge at Terminal 2 of NRT. Yes, you can enter any lounge you wish, more than one lounge. I have done lounge hopping at Terminal 2 before.

Admirals Club and Sakura Lounge have shower. And, yes, you can enter more than once. You can come and go, and come in again as you wish.

JAL Sakura Lounge upstairs dining area has best dining option out of all. Very limited but some dim sum selections at Cathay Business Class Lounge. Australian wine and newspaper at Qantas Lounge. What about Admirals Club at NRT…, it is a nice lounge, no complaint at all. Is there something unique about Admirals Club at NRT? No, but Admirals Club at NRT is nicer than the U.S. domestic Admirals Clubs.