What Tech Stack to simplify development?

I am building a website (currently under wraps) where visitors have two different journeys to sign up. Let's say 'Info seeker' and 'Info givers'.

The 'info seekers' will need to pay a small transaction to get info from the info givers. The info givers may or may not get a cut of that, but nonetheless, there are still small transactions.
Both will have user profiles. Both will have the ability to sign up and sign in with linkedin and email. And both will have a user dashboard after logging in.

The dashboards will have anonymous ways for the 'info seekers' to contact the 'info givers' based on the profiles of the 'info givers' and what kinds of industries they are experts in.

What advice am I looking for?

I am looking for advice is there are simplified API or tech stacks that I could use to build this website. Such as a user profile management API + an anonymous email API. Or maybe an email API that also handles a follow-up funnel based on responses or lack of responses.

I have built several websites in the past alongside freelancers and wanted to simplify the process while also making it a more delightful experience for the users.

##My current half-planned tech stack:
-Email for high volume -Zoho Zepto mail or Sendgrid

• Payment integration - Stripe
• Potential Newsletters - Ghost.org or...
• User management system -
• etc etc

Any advice on suggested or cool APIs that help out general website development similar to this would be appreciated.

##Thank you