Moonlight Nagara

I know that Seishun 18 for winter will be on sale on Dec. 1 to 31, 2017. And reservation for Moonlight Nagara starts 1 month before the departure date.

I will be visiting Kyoto and Osaka on December 29, 2017 to Jan. 3, 2018.
I plan to use the Seishun 18 on my Trip.

Can I reserve a seat in Moonlight Nagara on November 29, 2017 and pay only 520 yen for the reservation fee even thought I still don't have Seishun 18 at that time?

Doesn't the Moonlight Nagara only run in summer?

Looks like it will run this winter... http://jr-central.co.jp/news/release/nws002326.html

You can always buy only a reserved seat ticket, no matter how you plan to pay the base fare.

Although you can buy a reserved seat ticket without "18", BUT unfortunately, that plan is "impossible".

In that period is "super busy week" as "year-end" and "new year",
especially ML-Nagara's one will be sold out quickly within 60 min fr 10:00 am of sales date usual.
BC, some JR special member ship service can "pre-book" fr one week before,
those many pre-books also starts same time fr 10:00 am automatically,
so it is very hard "cut in" as online processing even if JR station ticket office staff has super skills like this.
https://youtu.be/DCrM4nIs9ns
(1st staff is not regular speed, 2nd staff fr 0:19 is so)

And, 10:00 am starts ticket is not only for "ML-Nagara",
other trains(for Shinkansen's reserved mainly) passengers are thinking same,
so you cannot reach ticket office on best time usual.

If already living in Japan, you should ask at near JR station with ticket office ASAP.
ML-Nagara's ticket sales in nation wide(no for out of Japan), no related train stop station's or not.

If you are student of major college in Japan, "seikyo(co-op)" with and they sale JR tickets, staff knows well.
http://www.univcoop.or.jp/activity/grad/grad2014-03.html
http://www.s-coop.net/english/