Chubu Trip in Autumn

I have a few questions here regarding my upcoming trip to Japan. I will arrive Nagoya Centrair International Airport and the flight is expected to land at 4.30pm. My question is:

a. IF I plan to take a direct bus from Centrair to Takayama and the bus leave at 5.00pm, do I have time to catch the bus? (I only have a backpack and no luggage).

b. I plan to cover Kanazawa, Shirakawa and Takayama with one night stay at each place, then head back to Nagoya. Is one day more than enough for each place?

c. Do I expect to see snow in any of these place around 25th November? Or it is still mainly colourful leaves?

d. I plan to visit Korankei as well. Is end of November the best time to visit Korankei? Do I expect to see the peak of the autumn colour?

Thanks and rgds.

a. IF I plan to take a direct bus from Centrair to Takayama and the bus leave at 5.00pm, do I have time to catch the bus? (I only have a backpack and no luggage).

That is probably way too tight of a transfer. Is there a later option in case you miss the 5:00 bus?

b. I plan to cover Kanazawa, Shirakawa and Takayama with one night stay at each place, then head back to Nagoya. Is one day more than enough for each place?

One day is probably good for Shirakawa-go and Takayama. Kanazawa would benefit from 2 days. Note that once you factor in your transportation time you'll have more like half a day in each spot.

c. Do I expect to see snow in any of these place around 25th November? Or it is still mainly colourful leaves?

In an average year Shirakawa-go has a little snow at that time. The rest may get a light dusting if any at all.

d. I plan to visit Korankei as well. Is end of November the best time to visit Korankei? Do I expect to see the peak of the autumn colour?

Yes and yes

http://www.japan-guide.com/e/e3316.html

a. IF I plan to take a direct bus from Centrair to Takayama and the bus leave at 5.00pm, do I have time to catch the bus? (I only have a backpack and no luggage).
That is probably way too tight of a transfer. Is there a later option in case you miss the 5:00 bus?
The last option should be an 8.00pm bus from Meitetsu Bus Station, bus arriving Takayama at 11.00pm (not sure if this is a good option though).

I would like to know is it true that Hirayu Onsen and Shin Hokata Onsen are closed on November? Means that I cannot visit these places during my trip?

The hot spring resort of those two places is open in winter. As long as the road is not closed to traffic in the snow, you can go there.

I think in Kourankei in the end of November, the best time to see the autumn leaves are past slightly, but in the place where it was to see how the last year, it's worth going.
The photo at the bottom of the page of the blog below is the place of last year.
http://www.hyakunensou.co.jp/asuke/2013/11/ (Japanese)

I have another question here.

According to Nohi Bus website below, passenger from Centrair to Takayama (direct bus) is entitled for special rates on buses to Shirakawa and Shin Hokata.

http://www.nouhibus.co.jp/english/centrair/index.html

My question is, if I am travelling on reverse direction, meaning from Takayama direct to Centrair, will I be entitled for that special offer as well?

Unfortunately, No, You won't.
Special offer of which are provided only passengers from Centrair. You will not be able to receive them when you buy a ticket for the bus at the Takayama.

Noted. Thanks a lot for your information.