Hi Antonio,
1.) Almost every element in Matukio has an CSS class / id you can use for CSS. Making it really easy to style them. (Never edit Matukio css files, add it to your templates css file, because of updates).
Additionally you can always create a Joomla template override.
2.) Yes you can just set max bookable place to zero and then the whole booking process is disabled.
3.) No the images are only for the event-list. In the event detail page you mostly want to use different (landscape instead of portrait) images, matching better there. You can just insert them into the Matukio description.
Kind regards,
Yves