The following file types can be converted to Slides: .ppt (if newer than Microsoft® Office® 95) .pptx .pptm .pps .ppsx .ppsm .pot .potx .potm .odp For more information on importing and converting files to Slides, see Get started with Slides

Yes, you can download Slides as other file formats such as Microsoft® PowerPoint® and Adobe® PDF documents. For a list of supported formats, see Get started with Slides.

By using the Version History in the File menu. Slides keeps all your drafts in one file, along with a record of who made which changes, so there’s no need to keep multiple copies of a file. See Switch to an earlier version of your file.

Yes, as long as this option has been enabled by your G Suite administrator. If it is, you can share any of your presentations with customers, suppliers, and others outside of your domain.  As a work around you could always download the presentation as a PowerPoint or PDF and attach it to an email. 

Yes. If you have existing Microsoft® PowerPoint® documents, you can edit them directly from Slides without converting them. If you’d like to use Slides collaboration features, such simultaneous editing with your team and targeted feedback comments, you can import PowerPoint files and convert them to Slides. For more information, see Get started with Slides.