Noooo not React! If you’re going to do that, do it for Stimulus or Vue. Maybe one of the reasons Stimulus hasn’t taken off is that there’s not a site like this to champion it and offer such a high level of educational resources.
I know it’s selfish, but personally I can’t stand working with React. Vue and Stimulus work much closer to the way my brain works when I think about front end components.
An amazing follow up for this would be how to use Heroku with RDS Postgres (and/or Redis), so that when you've outgrown Heroku, your data is already in AWS and you don't have to worry about migrating it when you make the switch!