I have worked a couple cycles in the Cuyahoga County B.O.E. in their count center.  All ballots go through this building (East 40th and Payne Ave.). 

In Ohio, mail-ins are checked and counted as they are received.  Those counts are recorded and released as soon as the polls close on election day.  It's probably the strategy to announce a big lead up front and discount other votes as they come in.  It won't work.  You are correct that all ballots are double checked against voter rolls and all mail in ballots are marked as voted on those rolls, so multiples are flagged and eventually tossed pending investigation.

Standard practice (State Law) is to securely store ALL ballots and count them again the week after elections to certify the election.  Cuyahoga County uses the Scantron system - anyone who has taken a standardized test and filled in an oval knows it.  The scanners at the polling places have two thumb drives (mirror RAID)  that holds the count for that scanner.  The election day counts are taken from these thumb drives, checked against each other for continuity, then stored securely.  The paper ballots are placed in storage as they come in from the polling places pending sorting.  The paper ballots are then sorted by precinct, and the certification count is done with these ballots.  The ballots are returned to storage in case of a recount request or other challenge.  I don't know the time period they are stored before disposal.

All steps in the count process are done with two people, one from each party or an independent and party registrant. 

The ballots themselves are kept in bankers boxes for each precinct, in a windowless cinderblock room within a heavy mesh steel cage.  The cage (padlock) and the door in the cinderblock wall (deadbolt) are double locked, (one for each party) and the keys are kept in a vault in the site manager's office. 

The only job I've worked with more security cameras is the Casino.