How worried should I be about unlevel floors/vibrations?
If you aren't seeing new cracks or other signs of this getting worse, it sounds like what you'd expect in an older house. Try supporting your bookshelf with some shims - it might just not be evenly supported where it is, and wobbling because it's unsteady.

You'll want to investigate your structure if you see:


new cracks forming
changes in floor leveling
problems operating doors or windows.


Unless that happens, don't worry! Enjoy your new house. And come up with some fun projects to do to it!