and don’t forget the easy to overlook stuff – have you changed the signs, have a clear plan to change business cards, seating arrangements, etc. Especially if you are changing a name, logo, image, the worst thing you can do on day one is have a bunch of people walking around with the old companies uniform or logos everywhere.
Another critical if the acquisition is coming with layoffs, it’s super importnat to communicate individual on day one but also have a statement go out to everyone left to inform them what has happened, how impacted employees have been supported and most clearly if the downsizing is finished.