For more information see: Should I install the 32-bit or 64-bit version of Office/Outlook?Note: Even when you are using the 32-bit edition of Office 2016, some add-ins might not be compatible yet with Office 2016.When you start Outlook for the first time after the upgrade, the startup could take some time.
I had her give me permissions to her calendar and when I had her assistant make a new meeting request it showed on mine and her assistants however never showed on the primary persons calendar unless we closed outlook and reopened it.
We do have cache mode enabled on all user mailboxes in the organization so that it will allow them to work in outlook right away without it taking so long to load.
You can check with the vendor of the add-in to verify its compatibility.
If you run into issues with Outlook after the upgrade, start with disabling your add-ins.
If you are upgrading from a version earlier than Outlook 2007 Service Pack 2, then several extensive file structure changes to the pst-file are being made which could take a lot of time (especially with a large pst-file).