I will be travelling to NRT from CLE on NH via either IAD or LAX.

The tickets on NH are free, and as such would be under a different PNR than the domestic segment from CLE to one of those cities (right?).

I'm going to be flying UA for the domestic portion, which leaves me with some questions:

(1) Is it possible to combine the two different PNRs into one, so I would be protected in the case of a cancelled/delayed flight? Is there some other way I should book this?

(2) Would it be possible to use my UA MP number for the domestic portion (because I have paid for E+) but my NH number for the international segments?

(3) Is this connection doable if I have two hours in ORD and three in LAX, or five hours in IAD? What happens if one of the flights is delayed, but the two portions of the trip are ticketed independently? Would I be better off arriving in LAX/IAD a day in advance?

This is my first time doing something like this, so please forgive my ignorance. Apologies in advance if I posted this in the wrong place; I assumed this would be best since it concerns more than one airline.

Thanks in advance for your help!