Here's my self-serving advice for every one-man SaaS: Use Heroku. It's super easy to get started. And when you reach $2000+ in monthly bills, hire me to move things over onto dedicated or EC2 so that you'll get 10x that performance for the same price. As for the actual language, I think PostgreSQL + Ruby Backend + JS Frontend is still the easiest way to get started. All those great architectural ideas don't matter mu…
I'd actually suggest PostgreSQL + Hasura + React with Ant Design or Material UI
I use this stack and I'm pretty sure I could pump out any SaaS business in about two weeks with it. Host on Heroku, use whatever analytics system you want.