Hi Julie,
It is hard to say what will happen when you update from a 5 year old version to the latest. Not many of us were around and the ones that are still around are not familiar with the latest coding.
I think the best thing to do would be to upgrade first to 2.0 then to 3.0 then to the latest.
As that should modify any of the fields in the database that were changed.
You may have to do that with Pro too. We would be able to provide older version of Pro if not available to you to do this.
You can get older version of the Events Calendar from here:
https://wordpress.org/plugins/the-events-calendar/developers/
I would test this out on a staging site first to see if you run into any issues.
Cheers!