Move Large Document Lirbary to new Site

Hi Community

I am looking for some guidance on a customer we are supporting. They have been a SharePoint online customer for a long time, well before we started working with them. Recently, they built a new Intranet using modern SharePoint hub sites and this has been working well for them.

Before they started this, they also had a single existing classic site with 5 subsets within the primary site. Each of these subsites reflected a department and, had a document library inside each of them. Each person then used the OneDrive "Sync" option to map this onto their PC or Mac and, they worked from their local device. One of these department's document libraries is 430GB in size.

The customer wants to achieve the following things:

1. Create a new SharePoint site which is connected as a hub site on their new intranet for this team and uses the modern theme/layouts they created.
2. Take one of the document libraries from the old site which is around 430GB and move it to this new SharePoint site - this is also going to have a new name for the department.
3. Selectively copy some of the data from the other subsite document libraries across to the new site - approximately 50GB

This is quite a complex move as we are going to have to break the sync on each user's computer after we check and ensure that all their changes have been synced from their local computers to the current document libraries. In addition, we will be recommending that they move from Sync to Shortcuts moving forward as recommended by Microsoft.

My question to the community is - what tool or method would you recommend that we use to move the main document library from one SharePoint site to a new SharePoint site? And also move approximately 50GB of data selectively from the other document libraries into this?

Thanks in advance for your suggestions and feedback.