I can't answer it for B2C, that growth might work different.
Start with a framework that includes authentication. It will save weeks of work. https://github.com/smirnov-am/awesome-saas-boilerplates
Good luck for your MVP/launch.
I believe they are listed in ~order of popularity/maturity by framework. Or at least the top 1-2 in each framework are the ones I've heard the most about.
Bullettrain (Ruby on Rails) is active on conferences, has a Dicord channel, his marketing approach is great.
Saas Pegasus (https://www.saaspegasus.com/) for Python/Django, Bullet Train (https://bullettrain.co/) and JumpStart (https://jumpstartrails.com/) for Rails, Spark (https://spark.laravel.com/) for Laravel, Gravity (https://usegravity.app/) for JS
You can find an even bigger list here: https://github.com/smirnov-am/awesome-saas-boilerplates though those are the market leaders (I make one of them and follow things closely)
That said, all of the popular boilerplates have been created by individuals or teams who are passionate about their frameworks (in my case Django) and have significant experience building products on top of them (in my case 10+ years). All of them will drastically reduce your time to MVP and likely be a better foundation than you'd author on your own.
I actually would choose a language/framework first and then choose a boilerplate based on that. The boilerplate will get you far, but ultimately you're still going to be doing lots more dev in the framework, so you should pick one you like. Django and Rails and to some extent Laravel are comparable - mature frameworks with lots of batteries included, mostly server-render HTML by default. JavaScript is its own separate beast with a more fractured ecosystem, but tighter integration with the front end. I'm obviously biased towards Python because it's a wonderful language to work with and has a great community and third-party package ecosystem. But honestly, any of these are great choices and will help you launch your first product way faster.
There's a huge list of SaaS boilerplates broken down by language available here: https://github.com/smirnov-am/awesome-saas-boilerplates
Good luck!
I know there's things like SaaS pegasus, but that forces Django. SaaS Pegasus and Bullet Train are also very expensive with no real options for trial. I wish tools like that - automating the basics of an ecommerce business - were more developed and available, preferably open source in the long run. I feel like it's the future we're slowly moving towards but we aren't there yet. We have widely-used open source frameworks for technical foundations - rails, django, etc - but no higher-abstraction equivalent that handles "features" like subscriptions and accounts.
It is infinitely easier to build and deploy things in 2020 than it was in 2010, and I'm hoping the time between now and 2030 represents a similar jump.
edit: found this list though https://github.com/smirnov-am/awesome-saas-boilerplates