Site collection size limit

Some things to consider:

1. If these files are no longer active, they could be archived on a File Share which SharePoint can index and then they will be findable using SP Search.

2. If you have compliance requirements, you may want to set up a dedicated Records Management site collection, see https://technet.microsoft.com/en-us/library/ee424394.aspx?f=255&MSPPError=-2147217396

3. if you don't have compliance requirements, a Document Center would be a good solution https://support.office.com/en-us/article/use-a-document-center-site-06096070-d83f-45b8-b02d-ec7a4cf85cac

4. Since this is  a high profile project, people with experience should be involved with planning the architecture and implementation techniques and they should then show you how to implement their plan.

5. Asking someone without SP experience to do this is unfair to you and not good management.