1. The blue flower crystals are in an area before the one of your screenshot. Go around and explore some more.
2. In that exact area where you need it. The underground fortress has two exits in the south, which both lead to different dungeons. You need to explore a bit, then you'll find what you need.
3. It requires Lace to be on her bad path as well, and that you help some guard in the lowest floor of the secret prison area to get some "plants" for the prison.
4. That scene also requires the plants I mentioned above.
5. No, there is no potions or trick. You just have to be fast, and with the right timing.