Hiroshima to Sapporo on the train - how?

I'm looking at going from Hiroshima to Sapporo with a JR pass (flying is not an option). I know I have 3 main options:
1) Hiroshima to Osaka + Twilight Express to Sapporo (know I will pay a supplement)
2) Hiroshima to Tokyo + Cassiopeia or Hokutosei to Sapporo (know I will pay a supplement)
3) The whole way on 'regular' trains without sleeper berths

Questions:
- Which route is more scenic a journey? (I know Twilight express is along the coast?)
- How far in advance do tickets for Twilight Express, Cassiopeia and Hokutosei book up (I would be looking for the cheapest sleeper)? I cannot book until I reach Japan and activate my JR pass (~2 weeks before I want to take the trip - will this be enough time?)
- Re: Twilight express, what days/times does it run? I want to take it in mid-June - is the schedule out yet? Where can I find it (Hyperdia doesn't seem to have it, and I can't find it on the English JR west site)
- Is trying to get there on a 'regular' train with no sleeper berths a huge hassle? Looks like I can depart 7:15am from Hiroshima and make it there by 10:56, with 4 stopovers.

thanks!

1) Hiroshima to Osaka + Twilight Express to Sapporo (know I will pay a supplement)
2) Hiroshima to Tokyo + Cassiopeia or Hokutosei to Sapporo (know I will pay a supplement)
3) The whole way on 'regular' trains without sleeper berths

Which route is more scenic a journey? (I know Twilight express is along the coast?)

The Twilight Express route is the most scenic. Depending on the season, it will be dark before your reach the scenic area.

How far in advance do tickets for Twilight Express, Cassiopeia and Hokutosei book up (I would be looking for the cheapest sleeper)?

It depends on the season and day. For busy days, they sell out within minutes after going on sale one month before travel date. On other dates, there might be vacancies until the day of travel.

Re: Twilight express, what days/times does it run? I want to take it in mid-June - is the schedule out yet?

In June 2010, it runs on Mondays, Wednesdays, Fridays and Saturdays through June 14, and then everyday from June 16 to June 30.

Is trying to get there on a 'regular' train with no sleeper berths a huge hassle?

No, not at all. But it is a very long journey.

Looks like I can depart 7:15am from Hiroshima and make it there by 10:56, with 4 stopovers.

That's right.

Thanks so much, Uji. That's very helpful. Can you provide a link to the website (even if in Japanese characters) that lists this in case I have future queries about the timetable?

I guess we'll just have to wait until we get to Japan, see if things are booked, and hopefully one of these 3 options will still be available.

Here is the timetable in Japanese:
http://www.jrhokkaido.co.jp/network/jikoku/jikoku1.html