If files that are part of the database (the NDFs) were actually deleted, your only option is to restore from backup.  That's not "corruption" such as can be (potentially, often...

Whether you need to have regularly scheduled stats updates depends on your data churn.  I think the cutoff point for when SQL will trigger an auto-update of stats is something...

Sigh.  My first thought when I read the news about who the "retiring" Equifax CEO "blamed" for the breach was "It wasn't me!  It was the one-armed IT guy!"

So came across an article on a new programming language someone's working on.  I wonder if it'd be possible to get a "wrapper" for TSQL so we could use it...

Re-iterating what Thom said:  Most likely you didn't select it during the install process.
Either start the installer and choose add features / components  and select "Management Tools - Complete"...

Where I work, security is fairly high on the list of priorities.  With that being said, even here things could be more secure.  Sure, I have a separate dedicated "admin"...