Getting N'EX Tickets?

I'm going to be buying the N'EX Tokyo Direct Ticket to get into Tokyo and I was wondering if I could just buy my return ticket at the same time. Also just in case I don't buy it there, where else can I buy N'EX tickets and reserve seats?
I've been to Japan before but last time they had the Suica and N'EX package so I had everything set right when I got there.

I'm going to be buying the N'EX Tokyo Direct Ticket to get into Tokyo and I was wondering if I could just buy my return ticket at the same time.

Assuming that your return journey takes place within one month, yes, you can. But there is no discount available for the return journey.

Also just in case I don't buy it there, where else can I buy N'EX tickets and reserve seats?

At any other JR ticket office in Japan, and a few ticket machines in the Greater Tokyo area that allow users to make seat reservations.

Thank you! My trip is only 10 days long so I'll just purchase my return tickets right away.

Contrary to a common misconception, there is really nothing special about the N'EX. It's a JR limited express train like any other, and anything you read about purchasing tickets for JR limited expresses applies to the N'EX as well. In particular, you can buy a ticket at any JR ticket office, anywhere in the country.

General tip: Outside of the airport stations, write what you want clearly on a piece of paper to help the ticket office staff.

I used an ATM-style ticket machine at Shibuya. It was either badged for N'Ex tickets or I pressed a button to choose them. The instructions were in English. It's just a few extra steps over buying an ordinary ticket or recharging your suica, as you have to choose a time and (if I remember) a seat. Just make sure you give yourself enough time to get to the platform, especially if you have luggage. Obviously you can do it further in advance.

A JR Limited Express reserved-seat ticket can be purchased at a ticket-vending machine of this type.
http://www.jreast.co.jp/mv-guide/demo/img/kenbaiki.gif
(Please make sure to purchase also a JR basic-fare ticket. Unlike a N'EX Tokyo Direct Ticket, your "Narita Express" reserved-seat ticket corresponds to an additional Limited Express charge only.)
Any JR station on Yamanote Line is equipped with at least one ticket-vending machine of this type; in some stations, you need to get into a JR Ticket Office to use one.

All "Narita Express" seats require reservation; if you have purchased your reserved-seat ticket but miss that "Narita Express" train (#), with that ticket you can take a substitute later same-day "Narita Express" train if any, but you cannot use any seat there.
Besides these restrictions, "Narita Express" is just like most other JR Limited Express.

#: Even in that case, while that designated train runs on the designated section, your seat reservation is valid, so no other passenger can reserve the seat.