Hi @Jay Paterson ,
According to my understanding, I found a checklist for you as below. However, due to that ShareGate is a third-party tool, we are not familiar with this product, so it is recommended that you consult the product provider for more detailed information.
Thanks for posting in the Q&A forum! :)
References:
https://sharepoint.stackexchange.com/questions/238097/direct-upgrade-from-sharepoint-2013-to-2019
https://www.gtconsult.com/sharepoint-migration-checklist
Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.
If the answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.