Question about trains

Shinkansen tickets can be purchased at ticket reservation offices inside JR Stations, and at designated vending machines inside JR stations.

If it were me, I'd just go with the local train which is 6x cheaper especially if I recall you are not getting a JR Pass.

If you want to take the Shinkansen just for the experience, be aware that they don't travel at full speed on such a short distance so the money would be wasted. You also don't really feel the speed while inside. The best way to notice the speed is to stand on the platform a few metres in front of a Shinkansen. By the time the end of the train goes by you it is a blur yet it doesn't even goes at 1/2 speed yet!

So with Suica & N'EX, I can simply purchase this upon arrival at Narita airport?

And can this be used to Shin-Yokohama?

Yes, it can!:)

Yes, but from your post, I don't think you are going direct from Narita Airport to ShinYokohama are you?

Suica and NEX is two parts, a Special narita express ticket and a Suica card. The Suica card can be used on pretty much every train in the area (including the ones that use PASMO).

If you don't go direct from Narita Airport to ShinYokohama, you can still use the Suica part of "Suica and N'ex) to ShinYokohama as well on another day.

Will be going from Narita to Hamamatsucho on the 15th December.

But from there want to travel around Tokyo, including to Saitama on the 16th, Shin-Yokohama on the 17th, 18th and the 21st.

Will also need to use the toei subway lines, tokyo metro, so is Suica the best option there?

1.Will also need to use the toei subway lines, tokyo metro.
Yes, you are right.

2.is Suica the best option there?
Yes, it is!

Hyperdia
http://grace.hyperdia.com/cgi-english/hyperWeb.cgi
Start point: Hamamatsucho
Destination: Urawamisono, Saitama Studium's closest station.

hi!
I'll stay in tokyo for a month/january.
I'll go to Yokohama,Kyoto, Kobe, Osaka, Himeji, Fukui and Kanazawa. The JR Pass is a good choice?
Thanks...