Our initial thoughts anyway, whether it works or not we'll see on the day:

Shinjuku to Akasuka
then Akasuka to Kamakura
then Kamakura to Akihabara
then back to Shinjuku (we'll be stuffed by then)

We will have a Tokyo Metro pass but some of the sections of the trips look like they are on JR lines (we won't have our JR pass valid yet, only the Tokyo Metro pass), and maybe some other lines or areas that Metro Pass doesn't cover.

What I'd like to know is what we do in these cases if we are unsure what our Tokyo metro pass covers on some parts (or all parts) of a particular train trip? ie what procedures do we carry out at the train stations? We want it as seamless as we can.

In any case, the longest part, which is Shinjuku (or Tokyo) - Kamakura, is definitely a JR line (not metro). So is the way back from Kamakura back (maybe through Tokyo station) to Akihabara.

So... actually for the day when you are traveling to Kamakura, it would not make much sense to use a Metro Pass.

Its all getting a bit confusing.

We were going to have a 2 way Limo bus and 2 day Metro pass - since we need both Limo bus tickets the metro pass part is practically free.

Having said that, the NEX/ Suica card isn't much more, and includes 1500Y worth of fares, which seems a fair bit isn't it since we will only have 2 days in tokyo.

The other thing the Suica might help us with is the last day before leaving we will be back in tokyo (without a pass if we get the 2 consequtive day metro pass) so if its still got value (or reload) we can use that too.

It might be tight though - the flight lands at 7pm, what are the chances it will take longer than 2hr 10min to get through customs and buy our pass? 10:10 is the last NEX train out from Narita.

Other thing is, we can't get a 'return' NEX to get back to the airport from Tokyo as part of the deal so we'll have to then put out more money for a return NEX or Limo bus....

From Shinjuku to Asakusa, it takes a bit longer but there is a Metro-only route to get there. (Take Metro Marunouchi line to Ginza, then change to Ginza line to Asakusa.) You can get back to Shinjuku the same way, Metro only. Shorter way will involve JR line.

OK, to go to Kamakura, sorry, you have the less expensive choice compared with JR:
http://www.japan-guide.com/e/e3115.html
So you can buy this (non-JR, non-Metro) pass to go to Kamakura from Shinjuku. (JR train costs more, and is not covered by Metro pass anyway.)

When you come back from Kamakura using the above pass, you will reach Shinjuku - from there, if you want to go Metro only, you can go Shinjuku - Ginza (Marunouchi line), then Ginza - Akiharabara (Hibiya line).

If you are planning all this in one day, it sounds a bit tight, though. Actually, Asakusa and Akihabara are relatively close, so it might make sense to allocate one day to this area (if you want to do some shopping there), and save Kamakura trip for another day.

The above is completely without the Suica. If you decide to go Nex & Suica + JR Pass, then:
- You can use JR + Metro to go from Shinjuku - Asakusa (faster than Metro only), then back.
- You can buy the Kamakura pass (please look at the link above) for the Kamakura portion.
- From Shinjuku, you can take JR to get to Akihabara.

And yes, if your JR Pass is valid for the day when you travel from Tokyo to Narita, you can use that for Narita Express as well.

JR routes between Shinjuku and Kamakura: Suica.
Enoshima Electric Railway [Enoden] between Kamakura and Fujisawa: PASMO.
Suica and PASMO are compatible as to their e-money systems for fare payment and for shopping.
With a Suica card / a PASMO card, you can take a ride within Suica - PASMO network, changing railroad operators three times or less.
There is no discount to fares in principle, but if plural routes are presumable on your ride when you exit the network, a fare for the cheapest route among routes by least operators applies.
- PASMO Use Guide for travelers (PDF file):
http://www.pasmo.co.jp/en/pdf/pasmo_traveler_E.pdf
(The network map in this guide doesn't show all the stations).

A Tokyo Metro pass covers sections on 9 Tokyo Metro lines, does not cover sections on 4 Toei Lines with line symbols A, I, S, E.
- Tokyo Subway Route Map (PDF file):
http://www.tokyometro.jp/global/en/service/pdf/routemap...

From Shinjuku area to Asakusa Sta. of Tokyo Metro:
Fare: 230 yen per adult; Time: about 40 minutes.
Nishi-Shinjuku (M07) / Shinjuku (M08) / Shinjuku-sanchome (M09)
| Tokyo Metro Marunouchi Line
(M13) Akasaka-mitsuke (G05): The same platform
| Tokyo Metro Ginza Line
(G19) Asakusa
I guess this route is the best as to transfer.
When you choose Ginza Sta., you have to go on a passageway above another Hibiya Line platform to make a transfer between the two lines.

From Shinjuku area to Akihabara Electric Town:
Maybe JR Yamanote Line's outer loop (via Ikebukuro) is better than JR Chuo & Sobu Lines. When you choose the latter, it may take a bit long to find Akihabara Electric Town Exit in Akihabara Sta.
Most shops selling electrical goods in Akihabara are on the west side of Yamanote Line. If you hope to see also shops on the east side, then your options include Metro route mentioned by AK. From Hibiya Line (H15) Akihabara Sta. platform, you can get out at Exit 3, taking elevators 2 times.

//

We are going to get a Nex/Suica and a Kamakura Enoshima Kippu.

I think its easier, without having to work out specific routes we can and can't take with the metro pass, and we don't have to stuff around buying tickets for parts of trips either.

The metro pass thing was a good idea until we realised our JR pass will get us back to Narita anyway so the 2 way 2 day metro pass was overkill.

We are willing to pay a little more for what I THINK will be the convenience of the Nex/Suica and Kamakura Enoshima Kippu.