you should be able to select column TabID and place a primary key constraint on it.
other indexes may improve performance, but should not affect function.

Foreign key constraints ensure, there are no tabs in a deleted portal, the others are not as important for tabs itself.
You should review *.log.resources files inside /providers/dataproviders/sqldataprovider folder, these changes shuld have happened in DNN 5.3, AFAIR.

Regarding the original issue, please alter definition of TabPath column in Tabs table to allow null. Hopefully, this will solve the issue.

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Cheers from Germany,
Sebastian Leupold

   

Speed up your DNN Websites with TurboDNN

Roy,
backup is always a good idea ;)
btw: I am currently working on a solution (for DNN 7.2 and up) to fix database issues

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Cheers from Germany,
Sebastian Leupold

   

Speed up your DNN Websites with TurboDNN

DNN706 Attempt to Create Page
Error Page Add
No Page Added

Error: is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Cannot insert the value NULL into column 'TabPath', table 'dotnetnuke455.dbo.Tabs'; column does not allow nulls. INSERT fails. The statement has been terminated. The 'AddTab' procedure attempted to return a status of NULL, which is not allowed. A status of 0 will be returned instead. ---> System.Data.SqlClient.SqlException: Cannot insert the value NULL into column 'TabPath', table 'dotnetnuke455.dbo.Tabs'; column does not allow nulls. INSERT fails.

 

Allow Nulls for TabPath

 

DNN706 Attempt to Create Page
Error Page Add
However … Page Added

Error: is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Cannot insert the value NULL into column 'IsDeleted', table 'dotnetnuke455.dbo.TabModules'; column does not allow nulls. INSERT fails. The statement has been terminated. ---> System.Data.SqlClient.SqlException: Cannot insert the value NULL into column 'IsDeleted', table 'dotnetnuke455.dbo.TabModules'; column does not allow nulls. INSERT fails. 

Thank you Sebastian!