Sorry for my English. It's not perfect!
1) If your friend has a visa "temporary visitor" in Japan (usually 15days to 90days visa), he will be able to use Japanrail pass. Please ask him to see this JR group website. There is a photo of immigration stamps. If he got another stamp, he will not be able to use Japanrail pass I'm afraid.
2) Are you going to Nagoya? It's my hometown!
Well, if you get japanrail pass, you can use bullet train to Nagoya. It will take about 1.5 hours. However, you won't be able to use the fastest bullet trains are called "Nozomi" and "Mizuho"
For more information, please check links below.
a: You can use japanrail pass straight away from Narita airport to Nagoya. You need to activate your japanrail pass in a JR ticket office. There are a couple of ticket offices in Narita airport. http://www.japanrailpass.net/eng/en009.html
Take Narita express (run by JR) to Tokyo station then take bullet train to Nagoya.
b: You can also use bullet train to Osaka and Kyoto from Nagoya station. Both places are really quick from Nagoya if you use bullet train. Less than 1 hour but it would be better to check last bullet train to Nagoya if you are planing to come back in same day. (around 9pm)
Other suggestions are
* Takayama: It will take about two hours from Nagoya.
Access: Take train is called "Limited Express WIDE VIEW HIDA" You only need your japanrail pass.
Nara: it was the first capital in Japan. it will take 2 to 3 hours from Nagoya. It is depends on the local lines.
Access: Take bullet train from Nagoya to Kyoto. Then take JR Miyakoji Rapid or other JR Nara local lines to Nara station. You only need Japan rail pass.
Kumano kodo: it is one of world heritages in Japan. If you plan to visit here, I recommend to stay in Kumano. Probably day trip is difficult.
Access: Take JR WIDE VIEW NANKI from Nagoya station to owase. After that, it is actually depends on you. Kumano kodo is an ancient walking route. You need to decide the starting point.
Ise shrine/ Ise jingu (Personally I would love to recommend this shrine than Kyoto! It is the biggest shrine in Japan. Seafood in this area is great! Prawns are big and you can have Japanese lobster "Ise Ebi")
Access: Take JR Rapid MIE from Nagoya station to ISE SHI/ ISE City. There is only a JR train per hour.
If you want to see Lavender, Hokkaido (Big island in North) is the best.
4) As you intend to travel for around 3 weeks, lets look at the 21 day rail pass as a guide first. The 21 day rail pass is ¥57,700, so you will need to spend at least that in individual tickets for it to be worth while. Here are the legs you are sure about:
- Narita airport terminal 1 > Tokyo: ¥2740, (62mins, 79km)
- Tokyo > Nagoya: ¥10380, (127mins, 366km)
- Nagoya > Kyoto: ¥5240, (37mins, 147km)
- Kyoto > Nagoya: ¥5240, (51mins, 147km)
- Nagoya > Osaka: ¥5980, (66mins, 190km)
- Osaka > Nagoya: ¥5980, (66mins, 190km)
- Nagoya > Tokyo: ¥10380, (107mins, 366km)
- Tokyo > Narita airport terminal 1: ¥2740, (58mins, 79km)
TOTAL: ¥48,680 for 8 legs
This means that you will need to spend at least ¥9020 in other trips to make a 21 day rail pass worthwhile. Many of the suggestions above will take you over this and will make a 21 day rail pass worthwhile.
A 14 day rail pass, at ¥45,100 will not cover your trips from Nagoya to Narita. As the trip from Nagoya to Narita is ¥13,120, you will have to pay a minimum of ¥58,220 if you go for this option, ¥570 more than a 21day pass! (14 day pass plus travel to Narita from Nagoya), and will also have to make extra trips to make the 14 day pass worthwhile.
A 7 day rail pass will only make sense if you aim to base yourself in Tokyo after the first week, as the costs of transport will become very high after the 7 days have elapsed. Also you will be rushing to fit everything in the first week. If you have time on your side I don't recommend this option.
Hope this helps!