Hi,
Which version of OneNote are you using? Are you using the OneNote desktop app which comes with Office or the OneNote app comes with Windows 10?
If you are using the OneNote desktop app, you can click the "Pin Notebook Pane to Side" icon to pin all notebooks in the left side pane.

If you are using the OneNote Windows app, you can right click in the left side pane, select
Navigation Panes, then select Show All.

>>Also wondering if it's sensible to consolidate all notebooks into one notebook called Customers and then each customer is its own section. Each section would probably have 5-20 pages depending on activity at the customer
Regarding this, it's not recommended to consolidate all notebooks into one if it's not required to do this. If the worst happens, the notebook become corrupted and you cannot restore it from the backup, it will be difficult to restore all your data. If you
leave your data in different notebooks, this will reduce the risk.
Hope this helps.
Regards,
Steve Fan
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