Hi Jeff,
I don't believe we exclude email invalid leads from that count - however, I'm in Support not Sales so I don't know all of the details on that. I've been told that we *do* exclude anonymous leads.
As for the unsubscribed leads, even if you delete them from your database, their email addresses remain marked as unsubscribed on the back end via our "durable unsubscribe" feature:
https://community.marketo.com/MarketoResource?id=kA650000000GxXxCAK
which will automatically unsubscribe a new lead if it has the same email address as a lead which was unsubscribed when it was deleted. So if you have no intent of using those leads again, it's safe to just delete them.
I hope that helps!