Yes. The official guidelines say “In unnumbered operas (Wagner, for instance), sometimes an act is the smallest entity you can enter”.
So feel free to merge all parts of an act in the main act work.
Note that operas are tricky since there’s no perfect solution, so the topic comes frequently on the forum, e.g. https://community.metabrainz.org/t/once-more-about-wagners-operas/457748
I think the same discussion occurred about Bach’s works. IMO titles should be in German with aliases in other languages.
Personnally I never attempt to fix globally this kind of things because I always think there might be a semi-automatized way to do it (fetch titles and aliases from wikidata?) But if you feel motivated please do it 
Indeed links to recordings are done through the works, so filling as many recording-work relations as possible is the most valuable
Have you looked at https://community.metabrainz.org/t/the-classical-editor-toolbox/295817/16 and past https://community.metabrainz.org/tag/community-cleanup ?