One caveat to that - If you buy a rail pass, you cannot take a Nozomi train. With the rail pass, you would need to take a Hikari to Osaka and change to another train for the journey to Hiroshima. It adds a connection and some time to the journey. The upside, as abmj-j explained, is that you can use it for unlimited travel on JR lines for another six days after you arrive.

Edit: I didn't realize (or maybe I've forgotten) that NRT-HND Limo Bus leaves every 10-15min. I thought they left a lot less frequently. That being the case, I think 4:00 NRT/HND transit is no riskier than 1:55 NRT/NRT transit.

If it were me, I'd take my chances on the NRT flight rather than HND. Under most circumstances, you'll be past the customs within an hour of landing. 1 hr includes taxiing and deplaning time. Then it's up to 10min walk to immigration, up to 20min passport control queue/process (could be longer here, but I think >20min is rare), up to 15min carrousel/customs. Of course, the flight could be late. But if it's <30min late, you'll probably be okay with the NRT connection.

I don't think 4hrs is safe for NRT-HND transit on 2 separate tix. I would still say 4hrs is not entirely safe for NRT-HND transit on 2 separate tix, although chances are you'll make it. It's safe on same tix. 3hrs definitely not safe even on same tix.

If you wanted to do shinkansen using Jpn Rail Pass (not Nozomi), then overnight in Shinagawa, then take the 8.10am Hikari to Shin-Kobe, transferring to 11.22am Hikari onto Hiroshima, arriving at 12.35pm.

Shinkansen would be your safest bet.

NRT
 

I have flown into NRT at least a dozen times...a couple were less time between flights than i liked...BUT, at that airport, there are many JAL people that will push you in the right direction...if you think that you will have a problem...ask one and they will hand carry you to your destination...or make you aware that you will have no problem. It is really one of the most friendly airports I have traveled through in all my years.

Just to circle back on this, I arrived early morning at NRT, had a 12 hour layover before my next connection. Went to the JAL First lounge in T2, had breakfast, showered, left one of my carry on bags in the storage locker and then asked the reception desk if I could leave the airport to go out to Narita village for a walk about.
One of the staff members kindly escorted me through the security checkpoint and once we got to the immigration desks at the very right hand side against the wall is a desk with a JL staff member, this handles things like Transit Visas or "Shore Passes" as they call them for passengers as a form needs to be filled out to the effect of that JL is sponsoring the transit visa due to an onward connection.
The staff person filled out the form (all in Japanese) with detailed form my passport and onward boarding pass and I was seen to by an Immigration officer. He asked no questions, he stamped my passport for 72 hour stopover and thenI left. Went to Narita village by train (10 mins away), roamed around for 4-5 hours, had lunch, visited the Buddhist temple there and then returned to NRT. Went through immigration and security with no issues and back in lounge in time for tea and snack. So, if anyone is in the same situation, then there is no issue, you can double back and if needed JL staff can help you.

NRT/NRT
Dom/Int

I'll be flying from CTS to NRT in Y, then onto JFK in J with a 95min layover in NRT. Both legs are on a single ticket with ANA. My questions are:

1. do I go through exit immigration at CTS or NRT?
2. do I have to go through security again at NRT?
2. will I have enough time to pick up a few boxes of Tokyo bananas before boarding my final leg? *very important* :D

Thanks in advance!

Exit immigration at NRT, Security Check at NRT. Unless the lines are crazy long in the souvenir shops, you should have no problems whatsoever in getting Tokyo Bananas.

ITM-NRT/NRT-SIN
DOM-INT Connection
Same PNR (JAL)

Would like to check in my bags at ITM all the way through to final destination (SIN). How far in advance should I reach ITM airport to ensure my luggage is checked through.

One hour ahead is plenty of time. ITM is a small domestic airport and it will only take you 10-15 minutes to get to your gate after checking in. You will see a special check-in section for passengers transferring to an international flight at NRT in the same area as the domestic check-in counters.

When arriving on domestic flights at NRT, there are passport control and security check for passengers connecting to international flights. You do not have to walk all the way to international check-in area on 4th fl. of the terminal building. However, those ANA domestic flights to NRT are usually occupied by passengers connecting to international flights at NRT. When domestic flights arrive then passport control and security for passengers to international flights can get little backed up. Do not worry too much, the line moves quick, just giving you heads up.

I am more worry about souvenir shops at the terminal to buy Tokyo Bananas. Not want to stereo type, but from my experience when there are multiple flights to China around same time then souvenir shops in the terminal can get very busy with people buying easily 20 – 30 boxes of sweets. I did experience 15 – 20 min. line of wait to buy stuff at a souvenir shop at the terminal.

Yup I'm one of those Chinese ppl that love their sweets! Thanks for the heads up, hopefully I'll get lucky with a short transfer line.

Good news! You can buy Tokyo Banana at Chitose Airport at Sapporo! Sapporo sweet souvenir Shiroi Koibito is available at airports at Tokyo so I thought may be…

You have to go to international terminal of CTS, 3rd fl. before passport control and security look for a souvenir shop “Snow Shop”. You should able to buy a box of eight Tokyo Banana for 1029 yen.

Just arrive at CTS little early and buy Tokyo Banana at CTS, this way you do not have to worry about having enough time to buy Tokyo Banana at NRT. :)

That's a great idea! Thanks!! I do love Shiroi Koibito too! :p :D

Thanks! I want to minimise time spent in ITM as we have a 2 hr connection in NRT thereafter.

JFK-HND RT J on NH
HND-CTS RT Y on NH (but on separate ticket)
international-domestic transfers

For each direction, is it allowed to through check the bags? Which baggage rule applies here, the international J or domestic Y?

Thanks!

They would be in their good right to give you domestic allowance for the Y ticket. In practical terms, they will most likely check luggage through and Thus you will get the J allowance. However, please note that even if the check the luggage through from JFK, you will have to claim your luggage at HND and take it through customs.