Since you'll be running JavaScript in the browser, it also uses Node.js for the backend. This allows you to use the same code for validation, business logic, etc, and it specifically has multiple patterns to encourage this.
It's all one bundle that you run locally (or on one machine in production, or two if you want to split out the DB, which I'd recommend). By default, it uses Docker to run locally, but I've included instructions to run it on bare-metal, if you choose. For subscriptions, I use Stripe, but I mean you gotta use _someone_ for that, and I found their API to be easiest to work with, and thus modify.
I specifically built it so that I wouldn't have to keep re-creating the wheel when I wanted to try out a new SaaS idea as just one person, so it should work just fine for someone who doesn't want to require a team, but it should also work well for people who do want to scale to teams: one of the core components is that you break up work into "features" which are directories that repeat the common subdirectories (api, lib, ui) and make it easy to keep commonly-used code together.
Full docs are available publicly on the site, and if you have any questions, I'm more than happy to answer!