Re: In Outlook, I can see the attachments in the appointment, so I was hoping for
the same in Android.
Android Calendar has no concept of "attachments on a calendar item".
Re: When I accept an invitation, the email is moved to the Deleted folder
Yes, this is standard Exchange logic when accepting from the email message. It's exactly the same in Outlook and Office 365 web mail.
To avoid this, you can click "View in Calendar" and accept the invite from there -- the email message will remain in your inbox. This too is same as in Outlook and Office 365 web mail.