@Boe Dillard Per your description, I understand you want to find a cloud storage solution to replace the old on-prem file server, is it right?
OneDrive is designed for individual use, with the occasional sharing of files. SharePoint sites are used to store files that have shared ownership where several people own the files and might collaborate on them. You can choose them based on your requirement.
The below lists the details about OneDrive and SharePoint:
For more information about setting up file storage and share in M365, you can refer to the article.
To set permission based on groups, you can create Azure AD Security Groups or Microsoft 365 groups, then grant the groups needed permissions.
About groups in Microsoft 365, you can refer to this article.
Please check if the above helps you, if any misunderstanding, please free feel to reply.
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