Point 1 can be fixed and the others are IMHO beyond the reach of Sigil, which has no control over the content of these messages on the pink background.
To ensure that the error text does not escape outside the pink frame – create or edit the custom_preview_style.css file in the Sigil Preferences folder. Where's the folder?
Open "Preferences" and click on the "Open Preferences Location" button in the lower left corner. It's there.
Add to custom_preview_style.css file this line:
Code:
html parsererror h3, html parsererror div {white-space: normal;}