Hi @neuropathy ,
Do you have bought the Volume license for Office 2019? If no, you need to get the Volume license from Volume License Service Center first, I suggest you download Microsoft Volume Licensing Service Center (VLSC) User Guide:
Microsoft Volume Licensing Service Center (VLSC) User Guide
These user guides show step-by-step instructions for how to register, view account details, download products and more from the Microsoft Volume Licensing Service Center (VLSC). They also include screenshots, technical support information, and a glossary.
And you can contact VLSC support from this web:
Contact Us
For the question:
I have some integrations and things I rely on that were built for Office 2010 (custom scripts). I'm hoping the new suite doesn't break everything...
Does anyone have suggestions for licensing in the most cost-effective way and upgrading safely from Office 2010?
Do you mean you don't want to remove Office 2010 from PC and install Office 2019 in the same PC?
I suggest you refer to this support article:
Office 2010 and Office 2013, 2016, or 2019 side by side
Hope it's helpful.
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