Keyword research-am i missing something?

Hi guys,

I started my own website about e-commerce, but the topic is so big i cant find a strategy.

Because either keywords are highly competitive because most of the times you are competing against ahrefs, semrush,shopify etc etc or i cant figure if the lower volume keywords are worth the effort.

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Am i supposed to write one post per keyword?

my head is spinning....

Thank you