@PhM - both of these already exist
Changing the case of a title or author can be done individually via a right-click when editing ->Change Case -> Titlecase. You can also switch titles in bulk using the bulk edit metadata dialog. I don't believe there is a way of changing author names in bulk though.
As for merging authors - you can identify such authors using the Find Duplicates
plugin. Then in the tag browser, rename the author so the names match for the ones you are genuinely sure are the same author.