To answer your questions:
1. No, nothing breaks if you just pick the targets.
2. Not all blessings are one-shot problem solvers. Some just open up opportunities that you wouldn't otherwise have, like The Devil for instance, which just tells you terrible secrets about people.
When I ran it +33% to +50% was enough obstacles, but if your group have all picked up easy-solve blessings then you might want to up that number a bit. Essentially, you want to force the players to think a bit about what they're doing rather than just spam win buttons.
3. My intent was that each shift should be used once -- a bunch of them don't make sense if they're used more than once -- but that you need room for reuse on some of them in case combat goes on for more than 4-5 rounds. In hindsight Financial Revenge and Game Face should definitely also come with the 'don't use this more than once' note that's attached to Predictable, just for clarity.