While performance is pretty bad, there are, generally speaking, two parties involved: The Game Creators with their game and the user with their knowledge and rig.
Chests were bugged on the first day (no yellow indicator) but fixed on the second. I saved before using the lockpick for the first time and tried a bit until I got the hang of it. Let go and try again if it trembles too much. You’ll be better in no time. If you’re on console however, Warhorse promised to look it over as it seems to be too hard.
On my first playthrough I didn’t find the horse either, but it’s inside the Talmberg Castle, the horse you rode from Skalitz. If there are seriously no horses at all inside Talmberg Castle, you should make a screenshot of the empty stables and send a bug report to Warhorse.
You don’t need a horse, however, you just need to leave Talmberg. A failed quest just means you found another way.
Actually I haven’t encountered a lot of bugs at all. Once got stuck in bushes, once in a furniture, once henry was sitting the other way, and the “game-saved-message-bug”. That’s all …