[enhacement] Fix typos in messages shown to users

Found while reading the code for !475, several messages have typos such as s/Sucessfully/Successfully. Running the grammar&english inspection on PyCharm shows a few other typos that can be easily fixed, improving how we display errors to users. This has a low priority, but it's quite easy to fix. Assigning 4.1.12, but we can move it to later if needed.