SharePoint List Automatic Indexing

[Leon Kuper]

In this article  there is the following Note: Automatic index creation when sorting in the modern experience is limited to lists and libraries with less than 20,000 items.

I am expecting to have about 15000 items (rows) in a list. 

Do I need to create indexes for column manually or that Automatic indexing does it for me?

My concern is 5000 items limitation in a list view.

And do I need to run "Reindex List" periodically?

Thank you in advance.

[#2]

I have imported an excel file with 12000 items into the Sharepoint List. The default view is All Items and I have not got any 5000 Threshold Errors, though. Probably this is because I didn't scroll (by 30 items in a batch) to the bottom.

The Automatic Indexing creates the first index and all subsequent indexes are created after sorting any columns (besides those that are not supported). So it is not necessary to create them manually.

But  List view threshold: 11282 items (list view threshold is 5000) is still there (in the list settings).

After some googling, I have found this article it helped me to realize  how ridiculous this 5000 throttle is. If I understand it correctly, to work with lists longer than 5000 items, I need to create separate views based on some filtering, but how am I supposed to know that that filter will return less than 5000 items? Microsoft proudly inform their users of 30 millions list  items limit ...

Having Excel files on Sharepoint online to mitigate this issue is not an option for me.