Holiday Rapid Mt Fuji 2

I'm currently in the midst of planning my next trip to Japan and one of the places I was thinking of visiting is the Fuji Five Lake region. If I do go there, the itinerary will either be a day trip on the 17th April,

or an overnight trip which will look like this:
16 April- Fly from Hakodate to Haneda Airport. Take the bus from the airport to Kawaguchiko station. Stay in the area overnight.
17 April-Head into Tokyo in the evening

I've got a few questions related to this:

1) Hyperdia tells me a the Holiday Rapid Mt Fuji 1&2 runs on the 17 April (Not sure if Hyperdia timetables are up-to-date yet). Is that correct, some old posts here and on other websites say this service runs seasonally while some others say it runs throughout the year but only on weekends?

2) Can I purchase the tickets for this service at any Midori-no-madoguchi in any JR ticket offices nationwide or can I only purchase this at Shinjuku? I'll be in Nagasaki, Osaka, Hokkaido prior to Tokyo.

1)
Update yet right, search again after mid MAR.
Now operated on every weekend whole year right.
HyperDia now supported until last 29 FEB. (not 28)

And...
Rapid 2(even number) is up route for Tokyo(Shinjuku or more far).
Rapid 1(odd number) is down route from Tokyo area to Kawaguichiko.

2)
This rapid now part of reserved 1 car of 6 about 60 seats,
left all 5 cars are non-reserved about 300 seats.
Mid APR no need reserved usual except if full blooming Sakura week.
Purchasing only "reserved seat ticket(520Y)" at any JR stn with ticket office(midori no-).
Reserved seat ticket sales start 10:00 am of just one month before from dep date.
(No online booking/sales from out of Japan)

But you cannot purchase "base fare ticket" Kawaguichiko to Tokyo(Shinjuku or,) in advance
bc until Otsuki is NOT JR section. (Fuji kyuko is not JR as railway company)
However, base fare ticket is no "sold out" purchasing at Kawaguichiko stn on the day
also until Tokyo as one paper ticket no worry.
https://en.wikipedia.org/wiki/Fujikyuko_Line
https://en.wikipedia.org/wiki/%C5%8Ctsuki_Station
No need transfering at Otsuki just direct operate by using JR's car.

If using by Suica/PASMO(or, IC card for transportation) possible payment for only base fare
from Kawaguichiko to Tokyo just touching 2 times ticket gate in/out.
At Haneda AP sales PASMO(by Keihin kyuukou) and Monorail Suica(by Tokyo monorail).
Provided regular Suica is by JR-East. (no sales at Kawaguchiko and Haneda AP)
At Kawaguchiko stn sales PASMO only. http://www.pasmo.co.jp/en/

Fujikyu' s official data is valid until 28 Feb, 2016.
http://www.fujikyu-railway.jp/train/jr_train02_2015sp.php

At this site, they says a seat ticket, needed only for a reserved car (only one, out of six cars in total), can be purchased either at
o Fujikyu stations (Only Kawaguchiko, Fujisan, and Tsuru-Bunka-Daigaku-Mae),
o JR East (Midori-no-Madoguchi, and VIEW Plaza), and
o major travel agencies (nationwide),
before one month before the boarding date.

So, if you want it, visit a travel agency somewhere in Japan after 16 Mar.

Thanks for the answers. I'll only arrive in Japan on the 5 April and that will be at Kansai airport with some time before a connecting flight. I'm assuming there's a travel agency at Kansai Airport I can ask with regards to booking this ticket?

If I do a day trip taking the Holiday Rapid 1 and the Holiday Rapid 2 back, would 5 hours be sufficient to see the essential places of interest around Lake Kawaguchiko?

I usually find a travel agency at a more populated area, such as in a department store, and near a train station. Just try to drop at the information desk at the airport.

A needed time for sightseeing highly depends on personal interests. I would stay Kawaguchiko for a better possibility to see Mt Fuji in the morning, though many do just a day trip. With this warm winter, shibazakura could bloom at the time of your stay.
http://www.japan-guide.com/e/e6906.html
http://www.shibazakura.jp/eng/