Fukuoka to Hokkaido by JR

if i use JR 14days rail pass to travel in Hokkaido in Dec, how should I plan my train trip to make it enjoyable?

I will be starting from Fukuoka. I do not mind to stop at Osaka or any point for short sight-seeing.

Can you recommend?

Just want to stay in Hokkaido for at least 10days before heading back to Osaka.

if i use JR 14days rail pass to travel in Hokkaido in Dec, how should I plan my train trip to make it enjoyable?

Visit places, that you are interested in:
http://www.japan-guide.com/list/e1101.html

The train trip from Fukuoka to Sapporo by Japan Rail Pass takes 16.5 hours. If you leave Fukuoka (Hakata Station) with the 6:31 hikari, you could make the trip within one calendare day, arriving in Sapporo at 22:56.

Back to Osaka is another 13.5 hour train ride.

I recommend to fly. Not only will you save a lot of time, but it is also likely to come cheaper, unless you travel after December 13, when many air pases become unavailable:
http://www.japan-guide.com/e/e2364.html

Yes, I would recommend flying. Sitting on the JR rail even with the upperclass Hikari is daunting. Your butt starts to get sore after the 4th hour! Plus, sometimes you may not like your seatmates on the train.

I did it twice the last two winters.
I started the train journey from Nagasaki( flew there from Tokyo). Made a few stops ( Fukuoka, Hiroshima, Osaka, Tokyo, Morioka, Akita, Aomori, Hakodate ) before reaching the northern tip of Hokkaido, Wakkanai town. In Hokkaido, I visited most of the cities and smaller towns by train. I flew back from Sapporo to Tokyo to catch the connecting flight home. I had two JR passes, one 14 days and 21 days and spent close to six weeks for each trip.
In order to enjoy the long train journey it is advisable to break it and make one or two stops enroute to Hokkaido. This again would depend on your schedules and priority.

I enjoyed the train journey so much that I am planning one more this winter with a different route - the west coast of Honshu --Hokuriku and Tohoku.

Enjoy your journey!

We plan to stay 3 nights in Otaru, any good recommendation?

Is it cheaper to go Niseko from Sapporo or Otaru?

Thank u.