Shinjuku to Shin-okubo Station

I will be arriving in NRT airport at about 11am on the 29 April 2015.

I guess I will board the 12+pm N'EX and arrive in Shinjuku 1 hr 20mins later, so slightly before 2pm.

Planning to transfer to JR Yamanote Line to take train to Shin-okubo station.

May i know if the train will be crowded at that timing? And also if both train stations is accessible for us as we have big luggage to lug around? Eg, escalators or lift.

Thanks!

May i know if the train will be crowded at that timing?

No, urban trains are generally not very crowded on national holidays. And even on regular days, 2pm is not a very busy time of the day.

And also if both train stations is accessible for us as we have big luggage to lug around? Eg, escalators or lift.

Shin-Okubo is one of the few JR stations in Tokyo that do not have escalators and elevators yet. But Narita Airport Station and Shinjuku Station have.

Here is a map of Shinjuku Station.
http://www.jreast.co.jp/e/stations/e866.html
Here is the pdf of the same content.
http://www.jreast.co.jp/e/stations/img/map_e/e866.pdf#search='shinjuku+station+map '
Certainly Shinjuku Station Crowded.
However, holiday daytime train is not crowded so.
It also might be good to go by taxi from Shinjuku Station.