[Nagoyankee]

1) It won't be too late unless the spring comes unusually early this year. The ski resorts in Hokkaido are generally open through the first week or so of April. I myself have skied in early April in Tomamu, if not in Niseko.

Niseko is a very well-known resort, so you should have fun there. That's where you see the most Australians in Japan, too.

2) If your main purpose is hiking, then Hokkaido may not be your best choice for late March. You might want to go someplace around or west of Tokyo. No need to go too deep down south. Remember that late March is the season for the cherry blossoms for the good two-thirds of the country.

3) There's a Koyasan specialist on JF. So let's wait till he comes on.

4) I'm not sure what the cheapest method is, but there's a bus service between Osaka and Aomori. The one-way fair is 4,100 ~ 8,500 yen depending on the type of bus and dates. From Aomori, you can take the boat to Hakodate, Hokkaido. The fair is 2,700 yen one-way.

5) Sorry I know nothing about the rail pass as I'm a resident. But I'm sure others will be replying.