Custom clearance at Narita

My flight will reach Narita terminal 2 at 10:40am and I have to catch 12:22pm NEX to Shinagawa (then to Nagoya then Takayama) so I can reach Takayama by 7pm. Would I have enough time to clear the custom, exchange JR pass and reserve seats etc?

If your plane lands on time, you have no problem to do all of the above. Immigration/customs at NRT is very quick these days.

I just went through immigration/custom at Narita 24 days ago. The lines weren't long. I went through in about 10 minutes. Waited only a few minutes for my luggage (business class). Unless there is a major delay, you should be able to make it.

Enjoy and have a safe trip.

I think you have enough time to transit if it is a scheduled flight.
I recommend you to go to Nagoya airport instead of going to Narita airport.

Customs should take around 10 or so minutes long as its not busy. Baggage around 5-15 minutes and when you exchange for the JR Pass it all depends on how busy they are.
Few weeks back when I went to exchange for my pass it took about 15 minutes.

You should be able to get all the tickets when you get your JR Pass.

(from Hyperdia)
12:22 Leave NARITA TERMINAL 2 on NARITA EXPRESS 22.

13:23 Arrive SHINAGAWA
(Go upstairs. It's a short way (50 feet?) to Shinkansen gate).

13:40 Leave on HIKARI 515.

15:19 Arrive NAGOYA on Track 17, transfer to Track 11.
(If you want to eat, buy a bento in the station and eat on the train.
If you don't know what to get, say "TORI BENTO" - that's chicken).

15:43 Leave on WIDE VIEW HIDA 15.

18:17 Arrive TAKAYAMA.

That's very nice information from all of you. Thank you so much!