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Many thanks for this, it's really helpful.

Thanks. I assume then that they have no weight with regards building domain authority (as opposed to in-context links from high quality websites)?

I would recommend to disable tags indexing as there are cases where you are multiple tags for same topic. You can index categories as mentioned above that they are more structure and define your website in some way. If you write custom excerpt for each post, it helps categories to have unique content  for each post except.

Great! Happy to hear that all worked out!

Will do, thanks.