You’re headed in the right direction. C#, asp.net, sql server is an excellent stack for development. It’s fast to build in, and boring, in the good sense of the word.
The last thing you want from a money making project is for the underlying tech to invent new work for you in terms of fixing things that break over the weekend, and rewriting your entire front end because your framework of choice just pushed a new release with breaking changes.
Better still, you know it already, which means you can build things so they don’t break.
I’ve written about this in the past:
https://www.expatsoftware.com/Articles/happiness-is-a-boring...
Good luck!