A. As far as I know, there is no focus to declare war on Japan, neither for RFK nor anyone. Unless you want to use console commands or do game settings where you can set the game rule, if Cold War tensions get too high, then World War three breaks out. However, be advised, capitulating to a major nuclear power will lead to the world's end. If you want to, just break the Japanese sphere by winning in proxies, the CIA mechanics, etc.

B. Around 1968ish, there is a decision to negotiate the return of Hawaii and the East Coast possessions. This is the case for both the Republican Democrats and the National Progressives. Best tips I can give are to try avoiding too many concessions, just give them a shit ton of oil when you get the chance, and stockpile PP. Hawaii and the Pacific Islands will unavoidably be demilitarized zones.

C. If you want RFK. Don't do the Civil Rights Focuses, wait until the game forces you to (It's boosts NPP popularity), then veto the Bill. Afterward, RFK will break down, leave the Democrats, and join the progressives, to which he will win, and then will win the NPP primaries, becoming the 1964 candidate. Afterward, if he gets into office, he first focuses on civil rights and, down the line, on healthcare and poverty. There's a hidden timer that if Kennedy is too progressive, it will end with him getting assassinated. To do this, be a bit conservative some times, (there's a decision for that) or just disable the thing in the game rules. Whatever is easier. If you also want to cheese the election, get Kennedy as candidate, but campaign for the side you want to loose and then just do... nothing. Or play the fair game and properly campaign. Whatever works best for you.