How to set up activation emails for your SaaS?

Hello everyone, We have a SaaS with autonomous onboarding of our users. A certain percentage of subscribers start to use our services, and then a small percentage start to use us in production and pay. For the moment, we send a single welcome email with our backend, but we'd like to send several depending on several scenarios (use of this or that feature, credit running out soon, product not used for X amount of time, etc.). We've got lots in mind. Sending these emails would depend on the user data we have in our databases. We have almost 10k subscribers a week. We're wondering which solution to choose for this: we know a bit about Hubspot (which we use as a CRM) and Brevo (ex-Sendinblue - which we use to send marketing newsletters). If you have any tutorials that explain all this clearly, that would be great! Thanks Taha | Eden AI (www.edenai.co)