I've really wanted to speedrun this game, but for optimal timing I need patch 1.2 for the wall glitch, and I have no idea where to download it and how to put it into my game.

download is in the "Resources" tab on the left. Just copy it into your Dishonored folder and overwrite.

Is it common for people to get a message that says "There was an error saving the game." and it gets stuck on a screen?

I've never seen that.

It only happens when i download the patch files