Hi @Asug I think if you will use klaviyo app in the shopify store then it can be manageable, if not then the easiest way to solve this solution is that you can use shopify email through which you can easily send the email to the customers with certain tags that you are adding after some time.
Shopify email can easily be managed through the shopify flow app as well and you can have the custom template in shopify email as well.
Shopify email gives you first 10,000 emails each month free. After, that pricing starts at $1/1000 emails per month.
Hopefully it will help you. If yes then Please hit Like and Mark it as solution!
If you still need any assistance then please feel free to ask the same.
Best Regards
Sahil