2 or 3 night hitchhiking trip up to Hokkaido?

I'm currently living in Shiga prefecture, and I'm planning on hitchhiking to Hokkaido during the spring break (late march/ early april). I am hoping to get there in about 3 or 4 days with some time to stop at a couple of places. I was previously thinking about working my way through Nagano and cutting up to Niigata, but I think I'm just going to go along the Japan Sea moving up to Fukui, and proceeding along the sea. I'm wondering where might a couple of good half day trips be somewhere along Niigata and then further up in Akita or Aomori.

Also, additionally, if anyone has any advice on places to go in Hokkaido during this time I would very much appreciate it.

With hitchhiking, you would never know how far you can travel in a day, or whether you can go (be taken) where you planned to go. Could you consider maybe long-distance buses, or possibly local trains, for inexpensive transport? They used to have this Seishun 18 Kippu that you could use to ride local (meaning non-limited express) JR trains all day for about 2,000 yen a day; do they still have that for the school breaks?

Perhaps doable. I would suggest you to YouTube and search for Kyde and Eric. Eric produced a series of videos on him hitchhiking in Hokkaido. Gives you some idea on how easy or hard it is. If you think it is a good idea then do it. But I agree, Hokkaido is a huge island and you just don't know where you will end up.