Short Trip, Shirakawa Go

I really want to visit and spend some night in Shirakawa Go.
My plan is to go straight to Shirakawa Go from Tokyo as soon as i arrived at Narita or Haneda airport.

My question :
1. When is the best time to visit Shirakawa Go while it's still covered in snow but safe to visit ( i worried about blizzard)?
2. Is there any cheap transport go to Shirakawa Go from Tokyo? If I must use Shinkansen, please give me suggestion is there any Pass that I can use to minimize my transport cost?
3. Is there any ryokan in Shirakawa Go? and how much it's cost ?
4. Are there any certain rules that I must obey when visiting Shirakawa Go?

If there are any important information beside of my question, I really appreciate for your help.
Thank you so much.

http://www.japan-guide.com/e/e5953.html

It would help if you read a little bit about Shirakawa-go while you wait for some answers to your questions. This website has a page here: http://www.japan-guide.com/e/e5950.html and this section tells you how to get there:
http://www.japan-guide.com/e/e5953.html

There is a local tourist information website as well: http://ml.shirakawa-go.org/en/
This site includes some accommodation options. In the FAQ section there is some advice about visiting during winter:

Snow falls annually in Shirakawa-go from December to March. Please check the current snowfall situation in Shirakawa-go using the live cameras and services such as Yahoo! Weather. Additionally, winter season temperatures may fall below freezing, even during the day. Please be sure to wear a warm coat and other appropriate clothing such as gloves. There are frequent accidents caused by slipping on snow and ice, even when snow is not actually falling. Please refrain from wearing heels, and use appropriate winter footwear such as snowshoes or boots. We also recommend wearing rainwear or a poncho, rather than using an umbrella when it is snowing.

There's even a manga guide to manners in Shirakawa-go: http://ml.shirakawa-go.org/en/manga/

Lots of information for you!

I have seen that link before and still cannot make a decision about transportation. And I got confuse too how to booked a Gashoo Zukuri in Shirakawa Go. I am sorry I asked too much, I am a beginner traveler

What exactly is confusing you about transportation?

You have 4 options from Tokyo.
1) Go to Toyama and take a bus.
2) Go to Kanazawa and take a bus.
3) Go to Shin-Takaoka and take a bus.
4) Go to Nagoya and take a bus.

And as the page says, going to Toyama and taking a bus from there is the fastest route.

Thank you so much for the kind assistance.
I really appreciate it, and it's really helpful.

Here's a website of Shirakawago Live Camera as below:
http://shirakawa-go.org/livecam/